U.S. Environmental Protection Agency 

Documentation of OMB Review Under Executive Order 12866 

Title of Action: 

Docket#: FRL#: RIN:

This action was submitted to the Office of Management and Budget (OMB) for review under Executive Order (E.O.) 

12866, titled Regulatory Planning and Review (58 FR 51735, October 4, 1993). Whenever EPA makes publicly available 

a regulatory action that was reviewed under E.O. 12866, section 6(a)(3)(E) of the E.O. directs the Agency to also: 

(1) Make available to the public a copy of the information that was provided to OMB’s Office of Information and 

Regulatory Affairs (OIRA) for review under the E.O., i.e., the text of the draft regulatory action and, if applicable, 

an assessment of the potential costs and benefits, as well as additional information for those actions that are 

determined to be economically significant under the E.O. (Information requirements are described in sections 

6(a)(3)(B) and (C)). 

(2) Identify for the public any substantive changes between the draft submitted to OIRA and the action that was 

subsequently issued, using a method that is complete, clear, and simple. 

(3) Identify for the public those substantive changes made at the suggestion or recommendation of OIRA.

For this regulatory action, were substantive changes made to information reviewed under E.O. 

12866? [Please check the appropriate answer.]

No. [In the docket, include the information identified in item (1) below.]

Yes. [In the docket, include the information identified in items (1) – (3) below.]

Accordingly, the Agency has included this form and the following information in the public 

docket for this regulatory action: [Please check the appropriate information.]

(1) A copy of the information that was provided to OIRA for review under the E.O. 

(2) Documentation of any substantive changes made to the draft regulatory text that was 

submitted to OIRA when compared with what was subsequently made publicly available.

The documentation is provided on the pages following this form. Changes made at the 

suggestion or recommendation of OIRA, if any, are clearly identified through attribution to 

OIRA. EPA has used one or more of the following methods to note changes: [Select the 

appropriate option(s).]

(a) Redline-Strikeout – A copy of the draft regulatory action submitted, using redlinestrikeout to show the substantive changes that were made.

(b) Hand Markup – A copy of the draft regulatory action submitted, using handwritten notes 

to show the substantive changes that were made.

(c) Note to the file - A document that identifies the substantive changes that were made, 

with page and paragraph references to the draft regulatory action that was submitted.

If you have any questions about this regulatory action or this documentation, please call the 

contact:

Name: Email: Phone: 

Revised 05/05/2010 

Definition of “Waters of the United States” Under the Clean Water Act

EPA-HQ-OW- 2011-0880 9901-47-OW 2040- AF30

Donna Downing CWAwaters@epa.gov 202–566–2428
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EO12866_CWA WUS 2040-AF30 NPRM Preamble and Rule_20130917

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 110.1, 112.2, 116.3, 117.1, 122.2, 230.3(s), 232.2, 300.5, part 300 App. E, 302.3 

and 401.11 

DEPARTMENT OF DEFENSE

DEPARTMENT OF THE ARMY, CORPS OF ENGINEERS

33 CFR Part 328.3(a)

[EPA-HQ-OW- 2011-0880; FRL_XXXX-X]

[RIN 2040-AF30]

Definition of “Waters of the United States” Under the Clean Water Act

AGENCIES: Environmental Protection Agency (EPA); and U.S. Army Corps of Engineers, 

Department of the Army, Department of Defense.

ACTION: Proposed Rule

SUMMARY: The Environmental Protection Agency (EPA) and the U.S. Army Corps of 

Engineers (Corps) are publishing for public comment a proposed rule defining the scope of 

waters protected under the Clean Water Act (CWA), in light of the U.S. Supreme Court cases in 

U.S. v. Riverside Bayview, Rapanos v. United States, and Solid Waste Agency of Northern Cook 

County v. U.S. Army Corps of `Engineers (SWANCC). Today’s proposal would enhance 
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protection for the nation’s public health and aquatic resources, and increase CWA program 

predictability and consistency by increasing clarity on the scope of “waters of the United States” 

protected under the Act. 

The agencies propose to define the waters of the United States for all sections of the

CWA to mean: traditional navigable waters (TNWs); interstate waters, including interstate 

wetlands; the territorial seas; impoundments of waters otherwise defined as waters of the United 

States; tributaries, as defined, to traditional navigable waters, interstate waters, or the territorial 

seas; adjacent waters, including wetlands; and, on a case-specific basis, “other waters” that have 

a significant nexus to a traditional navigable water, interstate water, or the territorial seas.

The agencies also propose to exclude specified waters from the definition of “waters of 

the United States.” The agencies are not proposing changes to the existing exclusions for waste 

treatment systems designed consistent with the requirements of the CWA. The agencies are not 

proposing any changes for prior converted cropland1

. The agencies propose, for the first time, to 

exclude by regulation certain waters and features over which the agencies have as a policy matter 

generally not asserted CWA jurisdiction.

Finally, the agencies retain the existing regulatory definitions for the terms “adjacent”

and “wetlands.” The agencies propose for the first time to define the terms “neighboring,”

“riparian area,” “floodplain,” “tributary,” and “significant nexus.”

 1 “Waters of the US’ does not include PCC, which is currently defined by USDA for purposes of the Food Security 

Act at 7 CFR 122.2. EPA and the Corps use the USDA definition for purposes of determining jurisdiction under the 

CWA.
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Today’s proposal requests public comment on issues associated with the agencies’ 

proposed regulatory definition of “waters of the United States.” This notice also solicits 

information and data from the general public, the scientific community, and tribal, state and local 

resource agencies on the aquatic resource, implementation, and economic implications of a 

definition of “waters of the United States” as described in the proposal. The goal of the agencies 

is to ensure the regulatory definition is consistent with the CWA, as interpreted by the Supreme 

Court, and as supported by science, as the agencies work to protect water quality, public health, 

and the environment.

DATES: Comments must be on or before ______, X days after publication in the Federal 

Register. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA–HQ–

OW–2011–XXXX by one of the following methods:

• Federal eRulemaking Portal: http://www.regulations.gov. Follow the instructions for 

submitting comments. 

• E-mail: ow-docket@epa.gov. Include EPA–HQ–OW–2011–XXXX in the subject line of 

the message. 

• Mail: Send the original and three copies of your comments to: Water Docket, 

Environmental Protection Agency, Mail Code 2822T, 1200 Pennsylvania Avenue, NW, 

Washington, DC 20460, Attention: Docket ID No. EPA–HQ–OW–2011–XXXX.
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• Hand Delivery/Courier: Deliver your comments to EPA Docket Center, EPA West, 

Room 3334, 1301 Constitution Avenue, NW, Washington, DC 20460, Attention Docket 

ID No. EPA–HQ–OW–2011–XXX. Such deliveries are accepted only during the 

Docket’s normal hours of operation, which are 8:30 a.m. to 4:30 p.m., Monday through 

Friday, excluding legal holidays. Special arrangements should be made for deliveries of 

boxed information. The telephone number for the Water Docket is 202–566–2426.

Instructions: Direct your comments to Docket ID No. EPA–HQ–OW–2011–XXXX. EPA’s 

policy is that all comments received will be included in the public docket without change and 

may be made available on-line at http://www.regulations.gov, including any personal 

information provided, unless the comment includes information claimed to be Confidential 

Business Information (CBI) or other information whose disclosure is restricted by statute. Do not 

submit information that you consider to be CBI, or otherwise protected, through 

http://www.regulations.gov or e-mail. The http://www.regulations.gov website is an “anonymous 

access” system, which means EPA will not know your identity or contact information unless you 

provide it in the body of your comment. If you send an e-mail directly to EPA without going 

through http://www.regulations.gov, your e-mail address will be automatically captured and 

included as part of the comment that is placed in the public docket and made available on the 

Internet. If you submit an electronic comment, EPA recommends that you include your name and 

other contact information in the body of your comment and with any disk or CD–ROM you 

submit. If EPA cannot read your comment due to technical difficulties and cannot contact you 

for clarification, EPA might not be able to consider your comment. Avoid the use of special 

characters and any form of encryption, and ensure that electronic files are free of any defects or 

viruses. For additional information about EPA’s public docket, visit the EPA
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Docket Center homepage at http://www.epa.gov/epahome/dockets.htm. 

Docket: All documents in the docket are listed in the http://www.regulations.gov index. Some 

information, however, is not publicly available, e.g., CBI or other information whose disclosure 

is restricted by statute. Certain other material, such as copyrighted material, is publicly available 

only in hard copy. Publicly available docket materials are available electronically at 

http://www.regulations.gov or in hard copy at the Water Docket, EPA Docket Center, EPA West, 

Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public Reading Room is open

from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone 

number for the Public Reading Room is 202–566–1744, and the telephone number for the Water 

Docket is 202–566–2426.

FOR FURTHER INFORMATION CONTACT: Ms. Donna Downing, Office of Water 

(4502–T), Environmental Protection Agency, 1200 Pennsylvania Ave., NW, Washington DC 

20460; telephone number 202–566–1783; e-mail address: CWAwaters@epa.gov. Ms. Stacey 

Jensen, Regulatory Community of Practice (CECW–CO–R), U.S. Army Corps of Engineers, 441 

G Street, NW, Washington, DC 20314; telephone number 202–761–5856; email address: 

stacey.m.jensen@usace.army.mil.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information
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A. Does This Action Apply to Me?

B. How Can I Get Copies of This Document and Related Information?

C. Under What Legal Authority is this Proposed Rule Issued?

II. Background

A. Executive Summary

B. The Clean Water Act and Regulatory Definition of Waters of the United States

C. Background on Scientific Review and Significant Nexus Analysis

A. Scientific Synthesis

B. Summary of Significant Nexus Conclusions

III. Proposed Definition of Waters of the United States

A. Summary of Proposed Rule

B. Traditional Navigable Waters

C. Interstate Waters

D. Territorial Seas

E. Impoundments

F. Tributaries

G. Adjacent Waters

H. “Other Waters”

I. Waters that are not Waters of the United States

IV. Related Acts of Congress, Executive Orders, and Agency Initiatives

A. Executive Order 12866: Regulatory Planning and Review

B. Paperwork Reduction Act
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C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination with Indian Tribal 

Governments

G. Executive Order 13045: Protection of Children from Environmental Health and 

Safety Risks

H. Executive Order 13211: Actions Concerning Regulations That Significantly 

Affect Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act

J. Executive Order 12898: Federal Actions to Address Environmental Justice in

Minority Populations and Low-Income Populations

K. Environmental Documentation

I. General Information (***to be added later)

A. Does This Action Apply to Me?

B. How Can I Get Copies of This Document and Related Information?

C. Under What Legal Authority is this Proposed Rule Issued?

The authority for this proposed rule is the Clean Water Act, 33 U.S.C. 1251, et seq.

II. Background

 A. Executive Summary
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The U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of 

Engineers (Corps) publish for public comment a proposed rule defining the scope of waters 

protected under the Clean Water Act (CWA), in light of the U.S. Supreme Court cases in U.S. v. 

Riverside Bayview Homes, Solid Waste Agency of Northern Cook County v. U.S. Army Corps of 

Engineers (SWANCC), and Rapanos v. United States. The purposes of the proposed rule are to 

ensure protection of our nation’s aquatic resources and make the process of identifying “waters 

of the United States” less complicated and more efficient. The rule achieves these goals by 

increasing CWA program transparency, predictability, and consistency. This rule will result in 

more effective and efficient CWA permit evaluations with increased certainty and less litigation. 

This rule provides increased clarity regarding the CWA regulatory definition of “waters of the 

United States” and associated definitions and concepts. EPA’s Office of Research and 

Development developed a report that synthesizes this scientific literature (from herein, 

“Report”). The Report is under review by EPA’s Science Advisory Board, and the agencies 

expect the rule will not be finalized until that review and the final Report are complete. This 

proposal is supported by a body of peer-reviewed scientific literature on the connectivity of 

tributaries, wetlands and open waters to downstream waters and the important effects of these 

connections on the chemical, physical, and biological integrity of those downstream waters. 

Appendix A summarizes and applies currently available scientific literature that is part of the 

administrative record for this proposal. Additional data and information likely will become 

available during the rulemaking process, including that provided during the public comment 

process, and by additional research, studies, and investigations that take place before the 

rulemaking process is concluded. At the conclusion of the rulemaking process, the agencies will 

review the entirety of the completed administrative record and determine at that time whether it 
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supports the conclusions of this proposed rule. The agencies will make any adjustments to the 

final rule deemed to be appropriate at that time. 

“Waters of the United States,” which include wetlands, rivers, streams, lakes, and the 

oceans, provide many functions and services critical for our nation’s economic and 

environmental health. In addition to providing habitat, rivers, lakes, and wetlands cleanse our 

drinking water, ameliorate storm surges, provide invaluable storage capacity for some flood 

waters, and enhance our quality of life by providing a myriad of recreational opportunities. A 

desire to protect these vital resources led Congress to pass the CWA in 1972 in order to restore 

and maintain the chemical, physical and biological integrity of our nation’s waters. Based upon 

decades of experience implementing the CWA’s programs, the lessons learned and existing 

science provide strong support for the regulatory and policy underpinnings of the proposed rule. 

The proposed rule was developed with a much greater understanding of the importance of all 

aspects of tributary, wetland, and lake systems and the ecological functions and services they 

provide.

The proposed rule will reduce documentation requirements and the time currently 

required for making jurisdictional determinations. It will provide needed clarity for regulators, 

stakeholders and the regulated public for identifying waters as “waters of the United States”, and 

reduce time and resource demanding case-specific analyses prior to determining jurisdiction and 

any need for permit or enforcement actions.

The Federal Water Pollution Control Act Amendments, now known as the Clean Water 

Act (CWA), were enacted in 1972. The objective of the CWA is to “...restore and maintain the 

chemical, physical, and biological integrity of the Nation’s waters.” Its specific provisions 

establish water quality standards as a benchmark for regulatory and non-regulatory programs to 
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achieve that primary objective for surface waters. Prior to the CWA, the Rivers and Harbors Act 

of 1899 protected navigation and protected waters from pollution. The 1972 Act was an

amendment to the Federal Water Pollution Control Act of 1948 with its subsequent amendments 

through 1970. The current jurisdictional scope of the CWA is “navigable waters,” defined in the 

statute as “waters of the United States, including the territorial seas.” The CWA leaves it to EPA 

and the Corps to define the term “waters of the United States.” Existing regulations (last 

codified in 1986) define “waters of the United States” as follows: 

(1) All waters which are currently used, or were used in the past, or may be susceptible to 

use in interstate or foreign commerce, including all waters which are subject to ebb and 

flow of the tide;

(2) All interstate waters including interstate wetlands;

(3) All “other waters” such as intrastate lakes, rivers, streams (including intermittent 

streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa 

lakes, or natural ponds, the use, degradation or destruction of which could affect 

interstate or foreign commerce including any such waters:

(i) which are or could be used by interstate or foreign travelers for recreational or 

other purposes; or 

(ii) from which fish or shellfish are or could be taken and sold in interstate or 

foreign commerce; or

(iii) which are used or could be used for industrial purposes by industries in 

interstate commerce.

(4) All impoundments of waters otherwise defined as waters of the United States under 

the definition;
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(5) Tributaries of waters identified in paragraphs (a) (1)–(4) of this section;

(6) The territorial seas;

(7) Wetlands adjacent to waters (other than waters that are themselves wetlands) 

identified in paragraphs (a) (1)–(6) of this section.

The U.S. Supreme Court addressed the scope of waters of the United States protected by 

the CWA in United States v. Riverside Bayview Homes (1985), which involved wetlands 

adjacent to a traditional navigable water in Michigan. In a unanimous opinion, the Court 

deferred to the Corps’ judgment that adjacent wetlands are “inseparably bound up” with the 

waters to which they are adjacent, and upheld the inclusion of adjacent wetlands in the regulatory 

definition of “waters of the United States.” The Court observed that the broad objective of the 

CWA to restore the integrity of the nation’s waters “... incorporated a broad, systemic view of 

the goal of maintaining and improving water quality ... . Protection of aquatic ecosystems, 

Congress recognized, demanded broad federal authority to control pollution, for ‘[w]ater moves 

in hydrologic cycles and it is essential that discharge of pollutants be controlled at the source.’ 

In keeping with these views, Congress chose to define the waters covered by the Act broadly.”

The issue of “waters of the United States” was addressed again by the Supreme Court in 

Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC)

(2001). In SWANCC, the Court addressed the question of CWA jurisdiction over isolated ponds 

that had formed at a proposed solid waste balefill site in Illinois. The Corps had asserted 

jurisdiction over the ponds based solely on the presence of migratory birds. In a 5-4 opinion, the 

Court held that “33 C.F.R. Section 328.3(a) (3) as clarified and applied to petitioner’s balefill site 

pursuant to the ‘Migratory Bird Rule’ ... exceeds the authority granted to [the Corps] under 404 

of the CWA.” The Court noted that in the Riverside case it had “found that Congress’ concern 
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for the protection of water quality and aquatic ecosystems indicated its intent to regulate 

wetlands ‘inseparably bound up’ with the ‘waters of the United States’” and that “it was the 

significant nexus between the wetlands and ‘navigable waters’ that informed our reading of the 

CWA” in that case. SWANCC did not directly address other parts of the regulatory definition of 

“waters of the United States.”

Five years after SWANCC, the Court addressed the scope of CWA protection for 

wetlands adjacent to tributaries of traditional navigable waters in Rapanos v. United States

(2006). In June 2006, the Justices issued five decisions with no single opinion commanding a 

majority of the Court. The plurality opinion, authored by Justice Scalia, stated that “waters of 

the United States” extended beyond traditional navigable waters to include “relatively 

permanent, standing or flowing bodies of water.” Justice Scalia indicated that the phrase 

“relatively permanent” includes “seasonal rivers” but not “streams whose flow is ‘coming and 

going at intervals ... broken, fitful ... or existing only, or no longer than, a day.” The plurality 

also concluded that only wetlands with a continuous surface connection to other waters of the 

United States are protected by the CWA. Justice Kennedy’s concurring opinion took a different 

approach than Justice Scalia’s. Justice Kennedy concluded that “waters of the United States” 

includes waters “that possess a ‘significant nexus’ to waters that are or were navigable in fact or 

that could reasonably be so made.” He stated that wetlands have the requisite significant nexus 

where they “either alone or in combination with similarly situated lands in the region, 

significantly affect the chemical, physical, and biological integrity of other covered waters more 

readily understood as ‘navigable.’” Kennedy’s opinion notes that such a relationship with 

navigable waters must be more than “speculative or insubstantial.” Justice Kennedy’s 

“significant nexus” test for CWA jurisdiction that he applied to adjacent wetlands also can and 
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should be applied to other categories of water bodies (such as tributaries to traditional navigable 

waters or interstate waters, or to “other waters”) to determine whether they are subject to CWA 

jurisdiction, either by rule or on a case-specific basis. Neither the plurality nor Kennedy opinion 

invalidated any of the regulatory provisions defining “waters of the United States.”

The proposed rule would revise the existing definition of “waters of the United States”

consistent with the science and the above Supreme Court cases. The proposed rule retains much 

of the structure of the agencies’ longstanding definition of "waters of the United States," and 

many of the existing provisions of that definition where revisions are not required in light of 

Supreme Court decisions. The agencies’ propose a rule which is clear and understandable and 

which protects the nation’s waters, consistent with the law and currently available scientific and 

technical expertise. Continuity with the existing regulations, where possible, will reduce 

confusion and will reduce transaction costs for the regulated community and the agencies. To 

that same end, the agencies also propose, where consistent with the law and their scientific and 

technical expertise, categories of waters that are and are not jurisdictional, as well as categories 

of waters and wetlands that require a significant nexus evaluation to determine whether they are 

“waters of the United States” and protected by the CWA. Finally, the agencies propose

definitions for some of the terms used in the proposed regulation.

Under the proposed first section of the regulation, (a), the agencies propose to define the 

“waters of the United States” for all sections (in particular, sections 311, 401, 402, 404) of the 

CWA to mean:

(1) All waters which are currently used, were used in the past, or may be susceptible to 

use in interstate or foreign commerce, including all waters which are subject to the 

ebb and flow of the tide;
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(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under 

this definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) 

through (5) of this section; and

(7) On a case-specific basis, “other waters”, including wetlands, provided that those 

waters alone, or in combination with other similarly situated waters, including 

wetlands, located in the same region, have a significant nexus to a water identified in 

paragraphs (1) through (3) of this section.

As discussed in further detail below, the rule would not change the following provisions 

(although some provisions have been renumbered): traditional navigable waters; interstate 

waters; the territorial seas; and impoundments of waters of the United States. In paragraph (a)(5) 

of the proposed rule, the agencies propose that all tributaries as defined in the proposed rule are 

waters of the United States, except for ditches under paragraph (b)(4) and (b)(5) of the proposed 

rule. As discussed further below, while tributaries are waters of the United States under the 

existing regulation, the rule would include a regulatory definition of "tributary" and the agencies 

propose that only those waters that meet the new definition are waters of the United States. 

In paragraph (a)(6) of the proposed rule, the rule would clarify that adjacent waters, 

rather than simply adjacent wetlands, are waters of the United States. The rule would further 

clarify the meaning of “adjacent” by defining one of its elements, “neighboring.” The related 

terms of “riparian area” and “floodplain” are also defined in the proposed rule. 
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The rule states that on a case-specific basis “other waters” that have a significant nexus to 

a traditional navigable water, interstate water or the territorial seas are “waters of the United 

States.” Unlike the categories of waters in paragraphs (a)(1) through (a)(6), which would be 

jurisdictional by definition, these “other waters” would not be waters of the United States by 

definition; rather, these “other waters” would only be jurisdictional provided that they have a 

significant nexus to paragraphs (a)(1) through (a)(3) waters. Therefore, the rule also includes a 

definition of "significant nexus."

In the proposed regulation the rule defines the following terms:

(1) Adjacent,

(2) Neighboring,

(3) Riparian area,

(4) Floodplain,

(5) Tributary,

(6) Wetlands, and 

(7) Significant nexus.

Under the 2008 guidance (and the Kennedy standard) the agencies use the significant 

nexus analysis for non-relatively permanent waters (generally ephemeral and non-relatively 

permanent intermittent streams), wetlands adjacent to non-relatively permanent waters and 

wetlands that do not abut relatively permanent waters. With this proposed rule, the agencies 

conclude, based on existing science and the law, that a significant nexus exists between 

tributaries (as defined in the proposed rule) of traditional navigable waters and of interstate 

waters, and between adjacent water bodies (as defined in the proposed rule) and downstream 

traditional navigable waters and interstate waters, respectively. Consequently, this rule 
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establishes as “waters of the United States,” all tributaries (as defined in the proposal), of the 

traditional navigable waters, interstate waters, and the territorial seas, as well as all adjacent 

waters (including wetlands). This will eliminate the need to make a case-specific significant 

nexus determination for tributaries or for their adjacent waters because it has been determined 

that as a category, these waters have a significant nexus.

The proposed paragraph (b) excludes specified waters from the definition of “waters of 

the United States.” Those waters and features that are not “waters of the United States” would 

be:

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act.

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; 

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 
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(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

The rule does not affect longstanding exemptions in the CWA for agriculture, 

silviculture, ranching and other activities and does not change existing regulatory exclusions for 

waste treatment systems designed consistent with the requirements of the CWA pertaining to 

prior converted cropland. Where waters are not jurisdictional, clearly no CWA regulatory 

provisions apply to them. Where waters would be determined jurisdictional under the proposed 

rule, applicable exemptions of the CWA would continue to preclude any application of CWA 

permitting requirements. For example, if “other waters” are aggregated and determined to be 

jurisdictional as similarly situated in the region, as described by Justice Kennedy, any exempt

actions that could affect those waters would remain outside the regulatory requirements of the 

CWA. Most of these exempted actions relate to agriculture and include: agricultural stormwater 

discharges, return flows from irrigated agriculture, normal farming, silvicultural, and ranching 

activities, upland soil and water conservation practices, construction and maintenance of farm or 

stock ponds or irrigation ditches, maintenance of drainage ditches, and construction or 

maintenance of farm, forest, and temporary mining roads.

The proposed rule is expected to reduce documentation requirements and the time it takes 

to make approved jurisdictional determinations, by decreasing the number of jurisdictional 

determinations that require case-specific significant analysis evaluations. It will improve clarity 

for regulators, stakeholders and the regulated public by defining certain categories of waters as 

“waters of the United States” that previously required case-specific analyses prior to establishing

CWA jurisdiction through the approved jurisdictional determination procedures. A 

comprehensive review of a growing body of scientific literature as well as the agencies’ growing 
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body of scientific and technical knowledge and field expertise lead the agencies to conclude that

it is reasonable to establish certain categories of waters that are jurisdictional by rule as they have 

a significant nexus to an (a)(1) through (a)(3) water, specifically tributaries to traditional 

navigable waters, interstate waters, or the territorial seas, and their adjacent waters and wetlands. 

Case-specific jurisdictional determinations will still be required for the “other waters” category 

in paragraph (a)(7) of the proposed rule, because that category of waters requires a site-specific 

significant nexus analysis to determine whether or not those waters are subject to CWA

jurisdiction. Science indicates that there is not enough information at this time to determine that

the majority of “other waters” have a significant nexus to traditional navigable waters, interstate 

waters, or the territorial seas. 

A review of the scientific literature, including EPA’s draft synthesis Report of the peerreviewed science, shows that tributaries and their adjacent waters play an important role in 

maintaining the chemical, physical, and biological integrity of traditional navigable waters, 

interstate waters, and the territorial seas and other jurisdictional waters because of their

hydrological and ecological connections to and interactions with those waters. Therefore, it is 

appropriate to protect all tributaries and adjacent waters, because the tributaries, their adjacent 

waters, and the downstream traditional navigable waters, interstate waters, and the territorial seas 

function as an integrated system. Water flows through tributaries to downstream traditional 

navigable waters, interstate waters, and the territorial seas, and that water carries pollutants that 

affect the chemical, physical, or biological integrity of the (a)(1) through (a)(3) waters, 

including water quality, fisheries, recreation, and other ecological services that are important to 

citizens. Waters adjacent to tributaries also provide ecological functions that, in conjunction with 

the functions provided by the tributaries they are adjacent to, have a significant influence on the 
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chemical, physical, or biological integrity of downstream traditional navigable waters, interstate 

waters, and the territorial seas. Examples of the important functions provided by adjacent waters 

are the sequestering or transformation of pollutants to reduce inputs to tributaries and 

subsequently to downstream (a)(1) through (a)(3) waters, water storage, and sediment trapping. 

Given the large scale systematic interactions that occur, and the substantial effects that result, 

between tributaries, their adjacent waters, and the downstream traditional navigable waters, 

interstate waters, or the territorial seas, a significant nexus exists that warrants making those 

categories of waters jurisdictional by rule. 

States and Tribes play a vital role in the implementation and enforcement of the CWA. 

Section 101(b) of the CWA states: “It is the policy of the Congress to recognize, preserve, and 

protect the primary responsibilities and rights of States to prevent, reduce, and eliminate 

pollution, to plan the development and use (including restoration, preservation, and 

enhancement) of land and water resources, and to consult with the Administrator in the exercise 

of his authority under this Act.” The definition of “waters of the United States” applies to 

decisions concerning whether a waterbody is subject to any of the programs authorized under the 

CWA. Of particular importance, States and Tribes may be authorized by the EPA to administer 

the permitting programs of Section 402 and 404. Forty-six States and the Virgin Islands have 

been authorized to administer the NPDES program under Section 402, while two States 

administer the Section 404 program. Additional CWA programs that utilize the definition of 

“waters of the United States” and are of importance to the States and Tribes include the Section 

311 oil spill program, the water quality standards and total maximum daily load programs under 

Section 303, and the Section 401 State water quality certification process. Under the CWA,

States and Tribes retain full authority to implement their own programs to more broadly or more 
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fully protect the waters in their State. Under Section 510 of the Act, unless expressly stated in 

the CWA, nothing in the Act precludes or denies the right of any State or Tribe to establish more 

protective standards or limits than the federal CWA. Many States and Tribes, for example, 

protect groundwater; some others may protect wetlands that are vital to their environment and 

economy but which are outside the jurisdiction of the CWA. Nothing in this proposed rule would 

limit or impede any existing or future State or Tribal efforts to further protect their waters. In 

fact, providing greater clarity regarding what waters are subject to CWA jurisdiction will reduce 

the need for permitting authorities, including the States and Tribes, to make jurisdictional 

determinations on a case-by-case basis, leaving them with more resources to protect their waters.

While the principal goal of this rulemaking is to improve clarity for determining 

jurisdiction under the CWA with the dual benefits of improving certainty and greater efficiency 

for determining whether waters are covered, there are other tools and approaches underway to 

increase efficiency as well. For example, EPA and the Corps are working in partnership with 

states to develop new tools and resources that have the potential to improve precision of desk 

based jurisdictional determinations at lower cost and improved speed than the existing primarily 

field-based approaches. EPA and the Corps are very interested in identifying other emerging 

technologies or approaches that would save time and money and improve efficiency for 

regulators and the regulated community in determining which waters are subject to CWA 

jurisdiction. The agencies specifically invite comment on this topic. 

The proposed rule will benefit the nation by helping to protect the services and functions 

these important waterbodies provide consistent with the overarching objective of the CWA.
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IIB. The Clean Water Act and Regulatory Definition of Waters of the United 

States

The Federal Water Pollution Control Act Amendments, now known as the Clean Water 

Act (CWA), were enacted in 1972. The objective of the CWA is to “restore and maintain the 

chemical, physical, and biological integrity of the Nation’s waters.” 33 U.S.C. 1251(a). Its 

specific provisions were designed to improve the protection of the nation’s waters provided 

under earlier statutory schemes such as the Rivers and Harbors Act of 1899 (“RHA”) (33 U.S.C. 

403, 407, 411) and the Federal Water Pollution Control Act of 1948 (62 Stat. 1155) and its 

subsequent amendments through 1970. The jurisdictional scope of the CWA is “navigable 

waters,” defined in the statute as “waters of the United States, including the territorial seas.”

CWA section 502(7), 33 U.S.C. 1362(7). The CWA leaves it to the agencies to define the term 

“waters of the United States.” Existing agency regulations define “waters of the United States”

as follows: 

(1) All waters which are currently used, or were used in the past, or may be susceptible to 

use in interstate or foreign commerce, including all waters which are subject to ebb and 

flow of the tide; 

(2) All interstate waters including interstate wetlands; 

(3) All other waters such as intrastate lakes, rivers, streams (including intermittent 

streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa 

lakes, or natural ponds, the use, degradation or destruction of which could affect 

interstate or foreign commerce including any such waters: (i) which are or could be used 

by interstate or foreign travelers for recreational or other purposes; or (ii) from which fish 

or shellfish are or could be taken and sold in interstate or foreign commerce; or (iii) 
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which are used or could be used for industrial purposes by industries in interstate 

commerce.

(4) All impoundments of waters otherwise defined as waters of the United States under 

the definition;

(5) Tributaries of waters identified in paragraphs (a) (1)–(4) of this section;

(6) The territorial seas;

(7) Wetlands adjacent to waters (other than waters that are themselves wetlands) 

identified in paragraphs (a) (1)–(6) of this section. 33 CFR 328.3(a), 40 CFR 230.3(s). 

Counterpart and substantively similar regulatory definitions appear at 40 CFR 110.1, 

112.2, 116.3, 117.1, 122.2, 232.2, 300.5, part 300 App. E, 302.3 and 401.11.

The regulatory definition of “waters of the United States” provides two exclusions from 

waters of the United States. Waste treatment systems designed to meet the requirements of the 

CWA and prior converted cropland are not “waters of the United States” under the agencies’ 

regulations. Under the regulations, “Notwithstanding the determination of an area’s status as 

prior converted cropland by any other Federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA.” 33 CFR 

328.3(a)(8).

II.C. Background on Scientific Review and Significant Nexus Analysis

A. Scientific Synthesis

EPA’s Office of Research and Development prepared a draft peer-reviewed synthesis of 

published peer-reviewed scientific literature discussing the nature of connectivity and effects of 

streams and wetlands on downstream waters (U.S. Environmental Protection Agency, 
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Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the 

Scientific Evidence, (Washington, D.C.: U.S. Environmental Protection Agency, 2013), from 

herein, “Report”). The draft Report provides a review and synthesis of the scientific information 

pertaining to chemical, physical, and biological connections from streams, wetlands, and openwaters such as oxbow lakes, to downstream larger water bodies such as rivers, lakes, and 

estuaries in watersheds across the United States and the strength of those connections. While the 

scientific literature does not use the term “significant nexus,” there is a substantial body of 

scientific literature on the chemical, physical, and biological connections between tributaries and 

adjacent waters and other waters and the downstream larger water bodies, and on the strength 

and the effect of these connections. Based on the literature, the Office of Research and 

Development was able to assess the types of connections between the tributaries and adjacent 

waters and the chemical, physical, and biological integrity of downstream traditional navigable 

waters or interstate waters. This proposed rule uses the information in the Report, other relevant 

literature, and the agencies’ technical expertise to make judgments about the nexus, or 

connections between the relevant waters, and the significance of the nexus for purposes of 

concluding that tributaries and adjacent waters, each as defined by the proposed rule, have a 

significant nexus as Justice Kennedy described such that they are appropriately jurisdictional by 

rule. 

The Office of Research and Development’s review and synthesis of more than a thousand

publications from peer-reviewed scientific literature focuses on evidence of those connections 

from various categories of waters, evaluated singly or in aggregate, which affect downstream 

waters and the strength of that effect. The scientific literature does not use the terms traditional 

navigable waters or interstate waters. However, evidence of strong chemical, physical, and 
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biological connections to larger rivers, estuaries and lakes applies to that subset of river, estuaries 

and lakes that are traditional navigable waters or interstate waters. The objectives of the Report 

are (1) to provide a context for considering the evidence of connections between rivers and their 

tributary waters, and (2) to summarize current understanding about these connections, the factors 

that influence them, and the mechanisms by which the connections affect the function or 

condition of downstream waters. The connections and mechanisms discussed in the Report 

include transport of physical materials and chemicals such as water, wood, sediment, nutrients, 

pesticides, and mercury; movement of organisms or their seeds and eggs; and hydrologic and 

biogeochemical interactions occurring in surface and groundwater flows, including hyporheic 

zones and alluvial aquifers. 

The EPA report concludes that the scientific literature clearly demonstrates that streams, 

regardless of their size or how frequently they flow, strongly influence how downstream waters 

function. Streams supply most of the water in rivers, transport sediment and organic matter, 

provide habitat for many species, and take up or change nutrients that could otherwise impair 

downstream waters. The Report also concludes that wetlands and open-waters in floodplains of 

streams and rivers and in riparian areas (transition areas between terrestrial and aquatic 

ecosystems) have a strong influence on downstream waters. The wetlands act as the most 

effective buffer to protect downstream waters from nonpoint source pollution (such as nitrogen 

and phosphorus), provide habitat for breeding fish and aquatic insects that also live in streams, 

and retain floodwaters, sediment, nutrients, and contaminants that could otherwise negatively 

impact the condition or function of downstream waters. Regarding wetlands and open-waters 

located outside of floodplains and riparian areas, the Report finds that they provide many 

benefits to rivers, lakes, and other downstream waters. If the wetland or open-water has a surface 
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or shallow subsurface water connection to the river network, it affects the condition of 

downstream waters. Where the wetland or open water is not connected to the river network 

through surface or shallow subsurface water, the type and degree of connectivity varies 

geographically, topographically, and ecologically, such that the significance of the connection is 

difficult to generalize across the group of waters.. Lastly, the Report concludes that to understand 

the health, behavior, and sustainability of downstream waters, the effects of small water bodies 

in a watershed need to be considered in aggregate. The contribution of material by a particular 

stream and wetland might be small, but the aggregate contribution by an entire class of streams 

and wetlands (e.g., all ephemeral streams in the river network) can be substantial. The Report’s 

conclusions, based on an examination of over a thousand peer-reviewed publications, provide 

support for policies in the proposed rule.

The Report is currently undergoing peer review by EPA’s Scientific Advisory Board 

(SAB) and is available at

http://yosemite.epa.gov/sab/sabproduct.nsf/fedrgstr_activites/Watershed%20Connectivity%20Re

port?OpenDocument. The agencies have identified key aspects of the Report throughout this 

preamble and in Appendix A. The Report summarizes and assesses much of the currently 

available scientific literature that is part of the administrative record for this proposal, and 

informs the agencies during this rulemaking. Additional data and information will become 

available during the rulemaking process, including that provided during the public comment 

process, and by additional research, studies, and investigations that take place before the 

rulemaking process is concluded. At the conclusion of the rulemaking process, the agencies will 

review the entirety of the completed administrative record, including the final Report reflecting 
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SAB review, to ensure that the administrative report supports conclusions of the final rule by 

making any adjustments that are necessary. 

B. Summary of Significant Nexus Conclusions

As the agencies developed this proposed definition of “waters of the United States,” the 

agencies carefully considered available scientific literature and propose a rule consistent with 

their conclusions that a particular category of waters either alone or in combination with 

similarly situated waters in the region, significantly affects the chemical, physical, and biological 

integrity of the traditional navigable waters, interstate waters, or the territorial seas. 

As discussed in this preamble and Appendix A, all tributaries as proposed to be defined

perform the requisite functions identified by Justice Kennedy for them to be considered, by rule, 

to be “waters of the United States.” Tributary streams exert a strong influence on the character 

and functioning of downstream traditional navigable waters and interstate waters, either 

individually or cumulatively. All tributary streams, including perennial, intermittent, and 

ephemeral streams, are physically and chemically connected to downstream traditional navigable 

waters and interstate waters via channels and associated alluvial deposits where water and other 

materials are concentrated, mixed, transformed, and transported. Headwater streams supply 

most of the water to downstream traditional navigable waters and interstate waters, and are the 

most abundant stream-type in most river networks. In addition to water, tributary streams supply 

sediment, wood, organic matter, nutrients, chemical contaminants, and many of the organisms 

found in downstream traditional navigable waters and interstate waters. Tributary streams are 

biologically connected to downstream traditional navigable waters and interstate waters by 

dispersal and migration of aquatic and semi-aquatic organisms, including fish, amphibians, 
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plants, and invertebrates, that use both up- and downstream habitats during one or more stages of 

their life cycles, or provide food resources to downstream communities. Chemical, physical, and 

biological connections between tributary streams and downstream traditional navigable waters 

and interstate waters interact via processes such as nutrient spiraling, in which tributary stream 

communities assimilate and chemically transform large quantities of nitrogen that would 

otherwise increase nutrient loading downstream.

Adjacent waters, as defined in this proposal, are chemically, physically, and biologically 

connected with the downstream traditional navigable waters and interstate waters they are 

adjacent to, or they are connected to traditional navigable waters or interstate waters through 

tributaries. These chemical, physical, and biological connections affect the integrity of 

downstream traditional navigable waters and interstate waters through the export of channelforming sediment and woody debris, storage of local groundwater sources of baseflow for 

downstream waters and their tributaries, and transport of organic matter. Wetlands and open 

waters located in riparian and floodplain areas remove and transform nutrients such as nitrogen 

and phosphorus. They provide nursery habitat for fish, and colonization opportunities for stream 

invertebrates. Adjacent waters, including those located in riparian and floodplain areas, serve an 

important role in the integrity of downstream traditional navigable waters and interstate waters

because they also act as sinks for water, sediment, nutrients, and contaminants that could 

otherwise negatively impact downstream traditional navigable waters and interstate waters . 

Finally, some non-adjacent waters may have, in certain circumstances, a significant 

nexus, but at this time the agencies are not proposing that a category of such waters is 

jurisdictional by rule. These “other waters” may provide numerous functions of potential benefit 

to downstream traditional navigable waters and interstate waters, including storage of 
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floodwater; retention of nutrients, metals, and pesticides; and re-charge of groundwater sources 

of river baseflow. The functions of these “other waters” may affect downstream traditional 

navigable waters and interstate waters, depending on the characteristics of the connection to the 

river network. For “other waters,” connectivity varies within a watershed and over time, making 

it difficult to generalize about their connections to, or isolation from, downstream traditional 

navigable waters and interstate waters. The literature reviewed did not provide sufficient 

information to evaluate the degree of connectivity of non-adjacent “other waters,” and therefore 

they will have to be evaluated on a case-specific basis under the proposed rule. 

Under the existing regulations, “other waters” (such as intrastate rivers, lakes and 

wetlands that are not otherwise jurisdictional under other sections of the rule) could be 

determined to be jurisdictional if the use, degradation or destruction of the water could affect 

interstate or foreign commerce. Jurisdictional decisions for these waters were made on a caseby-case basis. As a practical matter, the agencies generally relied on the presence of migratory 

birds to indicate an effect on interstate commerce. In 2001, the Supreme Court in SWANCC

rejected the use of migratory birds to establish jurisdiction over such intrastate waters. 

The proposed rule provides that “other waters” can be jurisdictional where there is a case 

specific showing of a significant nexus to traditional navigable waters, interstate waters, or the 

territorial seas. The concept of “significant nexus” is not a scientific term, and relies upon an 

analysis of the facts and circumstances of the waters being considered. 

As a general matter, all waters have a nexus to each other through the hydrologic cycle. 

However, as Justice Kennedy clearly stated, to establish jurisdiction under the CWA, there must 

be a “significant nexus” to traditional navigable waters. Justice Kennedy described that 

significance as something more than speculative or insubstantial. The support for a
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determination that the nexus is significant will be reasonable and based on a sufficient record 

that documents the scientific basis for concluding which functions are provided by the waters

and why their effects on a navigable water, interstate water, or the territorial seas are more than 

speculative or insubstantial. 

The agencies considered multiple options for determining how best to balance the science 

and the policy options available to address “other waters.” Those options ranged from 

establishing jurisdiction over all “other waters” with a nexus to traditionally navigable waters, 

interstate waters, or the territorial seas, because the agencies determined categorically the nexus 

to be significant, to declining to assert jurisdiction over any “other waters.” While proposing 

that all “other waters” are jurisdictional is not supported by the CWA as interpreted by the 

Supreme Court, a proposal that none of these “other waters” possess a “significant nexus” is not 

supported by the science, the CWA, or the Supreme Court. Scientific literature indicates that 

waters can have a relationship to each other that affects their chemical, physical, and biological 

integrity. This relationship is not an all or nothing situation. There is a gradient in the relation of 

waters to each other. The agencies propose a case specific analysis in establishing jurisdiction 

over these “other waters” as consistent with the current science, the CWA and the Supreme 

Court decisions, and it allows for a determination of jurisdiction where the gradient in the 

relationship becomes significant. 

The agencies also considered identifying subcategories of “other waters” that have a 

significant nexus to navigable waters and could be jurisdictional by rule. The Report indicates 

that there is evidence of very strong connections in some subcategories. The agencies solicit 

comment on making such subcategories of waters with very strong connections jurisdictional as 

a part of this rule. Such comment should explain with supporting documentation why a 
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particular subcategory of “other waters” might have a significant nexus to traditional navigable 

waters, interstate waters, or territorial seas.

Using absolute standards such as flow rates, surface acres, or a minimum number of 

functions to establish a significant nexus over “other waters” is not supported by the science and 

is inappropriate for a national rule addressing these “other waters.” A determination of the 

relationship of “other waters” to traditionally navigable waters, interstate waters, and the 

territorial seas across the nation, and consequently the significance to other waters, requires 

sufficient flexibility to account for the variability of conditions across the country and the varied 

functions that different waters provide. The case specific analysis called for in the proposed rule 

recognizes geographic and hydrologic variability in determining whether an “other water” or 

group of “other waters” possesses a “significant nexus” with traditional navigable waters, 

interstate waters, or territorial seas. 

III. Proposed Definition of Waters of the United States

A. Summary of Proposed Rule

Today’s proposed rule retains much of the structure of the agencies’ longstanding 

definition of “waters of the United States,” and many of the existing provisions of that definition 

where revisions are not required in light of Supreme Court decisions. The agencies’ goal is to 

promulgate a rule that is clear and understandable and protects the nation’s waters, consistent 

with the law and supported by science. Continuity with the existing regulations, where possible, 

will minimize confusion and will reduce transaction costs for the regulated community and the 

agencies. To that same end, the agencies also propose, where consistent with the law and 

supported by scientific literature, bright line categories of waters that are and are not 

jurisdictional. Waters in the “other waters” category are not a per se jurisdictional category 
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because current science does not support a conclusion that all “other waters” have a significant 

nexus to an (a)(1) to (a)(3) water or the identification of subcategories of “other waters” that 

would be jurisdictional by rule at this time. Therefore, the proposed rule requires a case-specific 

significant nexus evaluation to determine if such “other waters” are subject to CWA jurisdiction. 

Finally, the agencies are for the first time proposing definitions for some of the terms used in the 

proposed regulation.

Under the proposed paragraph (a) the agencies proposed to define the waters of the 

United States for all sections of the CWA to mean:

(1) All waters which are currently used, were used in the past, or may be susceptible 

to use in interstate or foreign commerce, including all waters which are subject to 

the ebb and flow of the tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States 

under this definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) 

through (5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those 

waters alone, or in combination with other similarly situated waters, including 

wetlands, located in the same region, have a significant nexus to a water 

identified in paragraphs (1) through (3) of this section. 
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As discussed in further detail below, the agencies do not propose to change the following 

provisions (although some provisions have been renumbered): traditional navigable waters 

((a)(1), see Section III.B of this preamble); interstate waters ((a)(2), see Section III.C of this 

preamble); the territorial seas ((a)(3), see Section III.D of this preamble); and impoundments of 

waters of the United States ((a)(4), see Section III.E of this preamble). In paragraph (a)(5), the 

agencies are proposing that tributaries to waters identified in paragraphs (a)(1) to (a)(3) are 

waters of the United States. As discussed further below, while tributaries are “waters of the 

United States” under the existing regulation, the agencies propose for the first time a regulatory 

definition of “tributary” and propose that only those waters that meet the definition and flow 

directly, or indirectly through “other waters,” to an (a)(1) through (a)(3) water are “waters of the 

United States” (see Section III.F of this preamble). In paragraph (a)(6), the agencies propose that 

adjacent waters, rather than simply adjacent wetlands, are waters of the United States. The 

agencies also propose for the first time to define an aspect of adjacency – “neighboring” – and 

related terms (see Section III.G of this preamble). Finally, the agencies propose to define 

“waters of the United States” to include “on a case-specific basis, “other waters,” including 

wetlands, provided that those waters alone, or in combination with other similarly situated 

waters, located in the same region, have a significant nexus to a water identified in paragraphs 

(1) through (3).” Unlike the per se jurisdictional categories in paragraphs (a)(1) through (a)(3) of 

this section of the proposed regulation, such “other waters” are not per se jurisdictional under 

(a)(7); rather, these “other waters” are only jurisdictional provided that they have a significant 

nexus to (a)(1) through (a)(3) waters. Therefore, the agencies are providing a definition of 

“significant nexus” (see Section III.H of this preamble).
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The second section of the proposed regulation, section (b), excludes specified waters 

from the definition of “waters of the United States.” Those waters and features that are not 

“waters of the United States” are:

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean 

Water Act, the final authority regarding Clean Water Act jurisdiction remains with EPA; 

and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry 

land and used exclusively for such purposes as stock watering, irrigation, settling basins, 

or rice growing; artificial reflecting pools or swimming pools created by excavating 

and/or diking dry land; small ornamental waters created by excavating and/or diking dry 

land for primarily aesthetic reasons; water-filled depressions created incidental to 

construction activity; groundwater drained through subsurface drainage systems; gullies 

and rills; non-wetland swales; and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section. 

With this section, the agencies are not proposing any changes to the existing exclusions 

for waste treatment systems designed consistent with the requirements of the CWA and for prior 
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converted cropland. The CWA and current regulations also provide a number of exemptions 

from permitting for specific activities. The rule does not affect any of the exemptions from 

CWA section 404 permitting requirements provided by CWA section 404(f), including those for 

normal agriculture, forestry and ranching practices. CWA section 404(f); 40 C.F.R. § 232.3; 33 

C.F.R. § 323.4. “Normal” agricultural activity is defined at 40 CFR § 232.3(c) and 33 C.F.R. § 

323.4. The rule also does not address the statutory and regulatory exemptions from NPDES 

permitting requirements for agricultural stormwater discharges and return flows from irrigated 

agriculture. CWA section 402(l)(1); CWA section 402(l)(2); CWA section 502(14); 40 C.F.R. §

122.3(f); 40 C.F.R. § 122.2 . The agencies are for the first time proposing to exclude by 

regulation in paragraph (b) certain waters and features over which the agencies have as a policy 

matter generally not asserted jurisdiction (see Section III.I of this preamble).

Finally, in section (c) of the proposed regulation the agencies define the following terms, 

of which “adjacent” “wetlands” are unchanged from existing definitions:

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section, 

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 
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structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and b(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.
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(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a) (1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a) (1) through (3) of this section. “Other waters,”

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a water of the United States so that they can be evaluated as 

a single landscape unit with regard to their effect on the chemical, physical, or biological 

integrity of a water identified in paragraphs (a) (1) through (a) (3) of this section. 

IIIB. Traditional Navigable Waters

EPA and the Corps’ existing regulations include within the definition of “waters of the 

U.S.” “[a]ll waters which are currently used, or were used in the past, or may be susceptible to 

use in interstate or foreign commerce, including all waters which are subject to the ebb and flow 

of the tide.” See, e.g., 33 C.F.R. § 328.3(a) (1); 40 C.F.R. § 230.3(s) (1); 40 C.F.R. § 122.2 

(“waters of the U.S.”(a)); 40 C.F.R. § 110.1(a) (“navigable waters”). The agencies do not 

propose to change this section of the regulation. These waters are often referred to as “traditional 

navigable waters.” The traditional navigable waters include all of the “navigable waters of the 

United States,” as defined in 33 C.F.R. part 329 and by numerous decisions of the federal courts, 

plus all other waters that are navigable-in-fact (for example, the Great Salt Lake, Utah, and Lake 

Minnetonka, Minnesota). Thus, the traditional navigable waters include, but are not limited to, 

the “navigable waters of the United States” within the meaning of section 10 of the Rivers and 

Harbors Act of 1899 (also known as “Section 10 waters”). See, Appendix B, Legal Analysis .
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For purposes of CWA jurisdiction, waters will be considered traditional navigable waters

if: 

• They are subject to section 9 or 10 of the Rivers and Harbors Act;

• A federal court has determined that the water body is navigable-in-fact under federal law;

• They are waters currently being used for commercial navigation, including commercial 

waterborne recreation (for example, boat rentals, guided fishing trips, or water ski 

tournaments);

• They have historically been used for commercial navigation, including commercial 

waterborne recreation; or

• They are susceptible to being used in the future for commercial navigation, including 

commercial waterborne recreation. Susceptibility for future use may be determined by 

examining a number of factors, including the physical characteristics and the capacity of 

the water to be used in commercial navigation, including commercial recreational 

navigation (for example, size, depth, and flow velocity), and the likelihood of future 

commercial navigation, including commercial waterborne recreation. While a traditional 

navigable water need not be capable of supporting navigation at all times, the frequency, 

volume, and duration of flow are relevant considerations for determining if a waterbody 

has the physical characteristics suitable for navigation. A likelihood of future 

commercial navigation, including commercial waterborne recreation, can be 

demonstrated by current boating or canoe trips for recreation or other purposes. A 

determination that a water is susceptible to future commercial navigation, including 

commercial waterborne recreation, should be supported by evidence.
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IIIC. Interstate Waters

The existing EPA and Corps regulations define “waters of the United States” to 

include “interstate waters, including interstate wetlands” and the agencies’ proposal today does 

not change that provision of the regulations. Interstate waters would continue to be “waters of 

the United States” even if they are not navigable for purposes of federal regulation under (a)(1) 

and do not connect to such waters. Moreover, because interstate waters are “waters of the United 

States” under the CWA, the agencies are proposing to continue to include tributaries to interstate 

waters, waters adjacent to interstate waters, waters adjacent to tributaries of interstate waters, and 

“other waters” that have a significant nexus to interstate waters.

As discussed in more detail in Appendix B to this preamble, the language of the CWA 

indicates that Congress intended the term “navigable waters” to include interstate waters without 

imposing a requirement that they be traditional navigable waters themselves or be connected to 

traditional navigable waters. The precursor statutes to the CWA always subjected interstate 

waters and their tributaries to federal jurisdiction. The text of the CWA, specifically CWA 

section 303 that establishes ongoing requirements for interstate waters, in conjunction with the 

definition of navigable waters, provides clear indication of Congress’ intent to protect interstate 

waters that were previously subject to federal regulation. Other provisions of the statute provide 

additional textual evidence of the scope of the primary jurisdictional term of the Act.

While congressional intent is clear, the agencies also have a longstanding regulatory 

interpretation that interstate waters fall within the scope of CWA jurisdiction. The agencies’ 

interpretation was promulgated contemporaneously with the passage of the CWA and is 

consistent with the statutory and legislative history of the Act. Furthermore, the Supreme Court 

has never addressed the CWA’s coverage of interstate waters, and its decisions in SWANCC and 
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Rapanos cannot be read to question the jurisdictional status of interstate waters or to impose 

additional jurisdictional requirements on interstate waters.

The precursor statutes to the CWA always subjected interstate waters and their tributaries 

to federal jurisdiction. While Congress intended tributaries to interstate waters to be subject to 

the CWA, the statute does not define the extent of tributaries that are covered. In light of Justice 

Kennedy’s opinion, it is reasonable to assert jurisdiction over tributaries, adjacent wetlands and 

other waters that have a significant nexus to interstate waters consistent with the framework 

established by Justice Kennedy in Rapanos for establishing jurisdiction over waters with a 

significant nexus to traditional navigable waters. Justice Kennedy’s standard seeks to ensure that 

waters Congress intended to subject to federal jurisdiction are indeed protected, both by 

recognizing that waters and wetlands with a significant nexus to traditional navigable waters and 

interstate waters have important beneficial effects on those waters, and by recognizing that 

polluting or destroying waters with a significant nexus can harm downstream jurisdictional 

waters. As Congress intended to protect interstate waters, the agencies propose to protect 

interstate waters by defining “waters of the U.S.” to include tributaries to interstate waters, 

waters adjacent to interstate waters, waters adjacent to tributaries of interstate waters, and “other 

waters” that have a significant nexus to interstate waters. For additional discussion of the 

agencies’ interpretation of the CWA with respect to interstate waters, see Appendix B to this 

preamble.

IIID. Territorial Seas

The CWA and its existing regulations include “the territorial seas” as a “water of the 

U.S.” The agencies propose to make no changes to that provision of the regulation other than to 
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move the provision to earlier in the regulation. The CWA defines “navigable waters” to include 

the territorial seas at § 502(7). The Act goes on to define the “territorial seas” as “the belt of the 

seas measured from the line of ordinary low water along that portion of the coast which is in 

direct contact with the open sea and the line marking the seaward limit of inland waters, and 

extending seaward a distance of three miles.” The territorial seas establish the seaward limit of 

“waters of the United States.” As the territorial seas are also clearly protected by the CWA, it is 

reasonable to use for protecting the territorial seas Justice Kennedy’s significant nexus 

framework that protects traditional navigable waters. The proposed rule reflects that.

IIIE. Impoundments

The agencies do not propose to make any changes to the existing regulatory language 

with respect to impoundments, “[i]Impoundments of waters otherwise defined as waters of the 

United States under this definition.” The Supreme Court has confirmed that damming or 

impounding a water of the United States does not make the water non-jurisdictional. See S. D. 

Warren Co. v. Maine Bd. of Envtl. Prot., 547 U.S. 370, 379 n.5 (2006)(“[N]or can we agree that 

one can denationalize national waters by exerting private control over them.”). Similarly, when 

presented with a tributary to the Snake River which flows only about two months per year 

because of an irrigation diversion structure installed upstream the Ninth Circuit has opined “it is 

doubtful that a mere man-made diversion would have turned what was part of the waters of the 

United States into something else and, thus, eliminated it from national concern.” U.S. v. Moses,

496 F.3d 984 (9th Cir. 2007), cert. denied, 554 U.S. 918 (2008). As a matter of policy and law, 

impoundments do not de-federalize a water, even where there is no longer flow below the 

impoundment. Where flow continues below the impoundment, it is straightforward to analyze 
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the stream network, above and below the impoundment, for connection to downstream 

traditionally navigable waters, interstate waters or the territorial seas. 

The agencies also note that an impoundment of a water that is not a water of the United 

States can become jurisdictional if, for example, the impounded waters become navigable for 

purposes of federal regulation under the Commerce Clause. Such a water would then be 

jurisdictional under paragraph (a)(1) of the regulation.

The existing agency regulations provide that impoundments of waters of the United 

States remain waters of the United States and the agencies do not propose any substantive 

revisions to that paragraph of the regulation. In addition, tributaries to an impoundment are 

waters of the United States under today’s proposed rule if the impoundment itself is a traditional 

navigable water or if the impoundment is of a water that is a tributary of a traditional navigable 

water, interstate water or the territorial seas. As a matter of law and science, an impoundment 

does not cut off a connection between upstream tributaries and a downstream (a)(1) through 

(a)(3) water, so tributaries above the impoundment are still considered tributary to a downstream 

(a)(1) through (a)(3) water even where the flow of water is impeded due to the impoundment. 

Scientific literature, as well as the agencies’ scientific and technical expertise, and practical 

knowledge confirm that impoundments have chemical, physical, and biological effects on 

downstream waters (see Appendix A, Scientific Analysis).

Appendix A discusses the conclusion that it is reasonable to maintain jurisdiction over 

impoundments of “waters of the United States” not only as a legal matter, but because 

impoundments do not sever the connections the impounded “waters of the United States” have to 

the physical, chemical and biological integrity of (a)(1) through (a)(3) waters.
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IIIF. Tributaries

Under today’s proposal, the agencies provide a definition of “tributary” supported by the 

scientific literature .The agencies also propose that all waters that meet the proposed definition of 

tributary are “waters of the United States” by rule, because tributaries and the ecological 

functions they provide significantly affect the chemical, physical, and biological integrity of 

traditional navigable waters, interstate waters, and the territorial seas. 

With today’s proposed regulation, the agencies confirm that these waters have a 

significant nexus to a traditional navigable water, interstate water, or territorial sea such that they 

are “waters of the United States” without the need for a separate, case-specific significant nexus 

analysis. Thus, in practice, under this proposal any water that meets the definition of tributary 

(and is not excluded under section (b)) of the proposed regulation) is a water of the United 

States. , and the agencies would only need to determine that a water meets the definition of 

“tributary.” See, Appendix A, Scientific Evidence and Appendix B, Legal Analysis.

Tributaries have a substantial impact on the chemical, physical, and biological integrity 

of waters into which they eventually flow—including traditional navigable waters, interstate 

waters, and the territorial seas --and they have a significant nexus and thus are jurisdictional as a

category. The great majority of tributaries are headwater streams, and whether they are perennial, 

intermittent, or ephemeral, they play an important role in the transport of water, sediments, 

organic matter, nutrients, and organisms to downstream environments. Tributaries serve to store 

water, thereby reducing flooding, provide biogeochemical functions that help maintain water 

quality, trap and transport sediments, transport, store and modify pollutants, provide habitat for 

plants and animals, and sustain the biological productivity of downstream rivers, lakes and 

estuaries.
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1. What is a “tributary” for purposes of the proposed regulation?

The proposed rule defines “tributary” as: 

Tributary: The term tributary means a waterbody physically characterized by 

the presence of bed and banks and ordinary high water mark, which contributes 

flow, either directly or through other waterbodies, to a water identified in 

paragraphs (a)(1) through (a)(3) of this section. A waterbody that otherwise 

qualifies as a tributary under this definition does not lose its status as a tributary 

if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the 

head of or along the run of a stream, debris piles, boulder fields, or a stream that 

flows underground) so long as a bed and banks and an ordinary high water mark 

can be identified upstream or downstream of the break. In addition, wetlands are 

tributaries (even if they lack a bed and banks and ordinary high water mark) if 

they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, 

including wetlands, can be a natural, man-altered, or man-made water body and 

includes waters such as rivers, streams, lakes, impoundments, canals, and ditches 

not excluded in paragraphs (b)(4) and (b)(5) of this section.

While the EPA and the Corps have not defined tributary in any previous regulation or 

preamble, this proposed definition is consistent with long-standing practice and historical 

implementation of CWA programs. It is important to note that today’s proposed definition also is 

based on best available science and the intent of the CWA.
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To meet this definition, a waterbody need not contribute flow directly to an (a)(1) through 

(a)(3) water. As the definition makes clear, the waterbody may contribute flow directly or may 

contribute flow to another waterbody or waterbodies which eventually flow into an (a)(1) 

through (a)(3) water. Essentially, the waterbody must be part of a tributary system that drains to 

an (a)(1) through (a)(3) water. Under the proposed definition, to be “tributary,” in addition to 

requiring that a waterbody contribute flow to a traditional navigable water, interstate water or 

territorial sea, the waterbody must also have a bed and banks and ordinary high water mark 

(except where a wetland is a tributary), because these features generally are physical indicators 

of flow. The agencies identified these tributary characteristics as indicative that the waterbody is 

the type of hydrologic feature Congress intended to protect under the CWA because, for 

example, of its ability to transport pollutants to downstream traditional navigable waters, 

interstate waters, or the territorial seas, and thereby have a significant effect on the chemical, 

physical or biological integrity of a water identified in paragraph (a)(1) through (a)(3).

The flow in the tributary may be ephemeral, intermittent or perennial, but the tributary 

must drain, or be part of a network of tributaries that drain, into an (a)(1) through (a)(3) water 

under today’s proposed rule. When considering whether the tributary being evaluated eventually 

flows to an (a)(1) through (a)(3) water, the tributary connection can be traced using direct 

observation or U.S. Geological Survey maps, aerial photography or other reliable remote sensing 

information, soil survey maps, or other appropriate information. A bed and banks and ordinary 

high water mark (OHWM) generally are physical indicators of water flow. These physical 

indicators can be created by ephemeral, intermittent or perennial flows. 

The agencies’ proposed definition of “tributary” includes waters such as rivers, streams, 

lakes, impoundments, wetlands, canals and ditches not excluded in paragraph (b)(4) or (b)(5)
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that, either directly or through other tributaries, convey water to traditional navigable waters, 

interstate waters, or territorial seas. A tributary is a longitudinal surface feature that results from 

directional surface water movement and sediment dynamics demonstrated by the presence of bed 

and banks structures, bottom and lateral boundaries, or other indicators of OHWM. The 

movement of water through a tributary can transport pollutants to downstream (a)(1) through 

(a)(3) waters, as either chemicals dissolved or suspended in the water column or adsorbed to 

sediment particles. The existing Corps regulations define OHWM as “that line on the shore 

established by the fluctuations of water and indicated by physical characteristics such as a clear, 

natural line impressed on the banks, shelving, changes in the character of soil, destruction of 

terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider 

the characteristics of the surrounding areas.” 33 C.F.R. § 328.3(e). This definition is not 

changed by today’s proposed rule. An OHWM may form in waterbodies, but the presence of an 

OHWM does not automatically identify waterbodies as “waters of the U.S.” In many tributaries, 

the bed is that part of the channel below the OHWM, and the banks often extend above the 

OHWM. Indicators of an OHWM may vary from region to region across the country. 

Under this proposed definition of tributary, the upper limit of a tributary is established 

where the channel begins, unless a wetland tributary is providing flow into the tributary at the

upper limit of the channel. While the OHWM generally defines the lateral limits of a water, its 

absence can be a factor in determining whether a tributary’s channel or bed and banks has ended 

such that the upper limit of the jurisdictional tributary is identified. However, a natural or manmade break in bed and banks or OHWM does not constitute the upper limit of a tributary where 

bed and banks or OHWM can be found farther upstream, as discussed below. 
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In many tributaries, there are often natural or man-made breaks in the presence of a bed 

and banks, or ordinary high water mark, while hydrologic connectivity remains. In some regions 

of the country, for example where there is a very low gradient, the banks of a tributary may be 

very low or may even disappear at times. Also, in many intermittent and ephemeral tributaries, 

including dry-land systems in the arid and semi-arid west, OHWM indicators can be 

discontinuous within an individual tributary due to the variability in hydrologic and climatic 

influences. The agencies proposed definition of “tributary” addresses these circumstances and 

states that waters that meet the definition of tributary remain tributaries even if such breaks 

occur. A waterbody that otherwise qualifies as a tributary under the proposed definition does not 

lose its status as a tributary if, for any length, there are one or more man-made breaks (such as 

bridges, culverts, pipes, or dams), or one or more natural breaks (such as debris piles, boulder 

fields, or a stream segment that flows underground) so long as a bed and banks and an ordinary 

high water mark can be identified upstream or downstream of the break. The presence of a bed 

and banks and an ordinary high water mark upstream or downstream of the break generally 

demonstrates continuity of flow. A water remains a tributary even if the channel, bed and banks, 

or OHWM disappears for a portion of the tributary provided a bed and banks, and OHWM can 

be found upstream or downstream of the break. 

Waters that meet the definition of tributary under the proposed rule are jurisdictional even 

if there is an impoundment at some point along the connection from the tributary to the (a)(1) 

through (a)(3) water. 

The proposed definition at (c)(5) provides that a tributary does not lose its status as a 

tributary if, for any length, there are one or more man-made breaks, such as dams. The existing 

regulation defines tributaries to impoundments and tributaries to the current (a)(3) “other waters”
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(i.e., “...intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, 

wetlands, sloughs...” 33 CFR 328.3 (a)(3)) as “waters of the United States” as well as tributaries 

to traditional navigable waters, interstate waters, and the territorial seas as “waters of the United 

States.” The proposed regulation clarifies that tributaries must be tributaries of an (a)(1) through 

(a)(3) water. However, a water would not be considered tributary under this proposal if it only

were a tributary to an impounded “other water” as defined under proposed new section (a)(7) 

(see Section III.I of this preamble). Such a water could be jurisdictional under (a)(7) of today’s 

proposal, but it would not be jurisdictional by rule as a tributary. Similarly, not all ditches are 

jurisdictional. Ditches that do not contribute flow, either directly or through other waterbodies, 

to a water identified in paragraphs (a)(1) through (a)(3) of this section are excluded from 

jurisdiction as “waters of the U.S.”

Longstanding agency practice has identified tributaries as including “natural, man-altered 

or manmade” waterbodies. Natural, man-altered, or manmade tributaries provide many of the 

same functions, especially as conduits for the movement of water and pollutants to other 

tributaries or directly to traditional navigable waters, interstate waters, or territorial seas. As 

conduits for water flow, they can help transport organisms, pollutants, and other substances, to 

the tributary system to traditional navigable waters, interstate waters, or territorial seas. The 

discharge of a pollutant into a tributary generally has the same effect downstream whether the 

tributary waterway is natural or manmade (see further discussion below and Appendix A).

Indeed, given the extensive human modification of watercourses and hydrologic systems 

throughout the country, it is often difficult to distinguish between natural watercourses and 

watercourses that are wholly or partly manmade or man-altered. For example, tributaries that 

have been channelized in concrete or otherwise have been human-altered, may still meet the 
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definition of tributaries under the agencies’ proposed regulation so long as they still contribute 

flow to an (a)(1) through (a)(3) water. The agencies’ proposed definition of tributary provides a 

non-exclusive list of the types of waters, natural, man-altered or man-made that may be 

tributaries: wetlands, rivers, streams, lakes, impoundments, canals, and ditches not excluded in 

paragraphs (b)(4) and b(5) of the proposed rule.

Under the agencies’ proposal, when a tributary flows through a wetland into another 

tributary (e.g., a run-of-stream wetland), losing its OHWM through the wetland, it remains a 

tributary, and the wetland itself is considered a tributary. Wetlands may contribute flow to a 

stream or river through channelized flow or diffuse flow, and sometimes both. Wetlands may 

also serve as water sources at the upper limit of headwater streams, where the channel begins. In 

light of their potential to be important contributors of flow to tributaries to traditional navigable 

waters, interstate waters or territorial seas, the agencies propose a definition of tributary which 

includes such wetlands. In other instances, wetlands may serve as the connection between a 

tributary and another tributary or even a traditional navigable water, interstate water or the 

territorial seas. For wetland tributaries, water may flow through braided channels that also 

include wetlands or through a run-of-stream wetland that does not have a bed and banks and 

OHWM.

Tidal ditches are subject to the ebb and flow of the tide and thus jurisdictional under 

section (a) (1) of the existing and the proposed regulation. The agencies are proposing to clearly 

exempt from the definition of waters of the United States two types of ditches: “ditches that are 

excavated wholly in uplands, drain only uplands or non-jurisdictional waters, and have no more 

than ephemeral flow; and ditches that do not contribute flow, either directly or through other 

waterbodies, to a water identified in paragraphs (a) (1) through (a) (3) of this section.” This 
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proposal generally does not change the agencies’ current practice with respect to ditches, but 

does for the first time codify these practices in regulation. In a 1986 Corps preamble and a 1988 

EPA preamble, the agencies each stated that they generally do not consider the following to be 

waters of the United States: “Non-tidal drainage and irrigation ditches excavated on dry land.” 

51 FR 41217 (1986), 53 FR 20764 (1988). In the existing 2008 Rapanos guidance, the agencies 

stated that they generally would not assert jurisdiction over “Ditches (including roadside ditches) 

excavated wholly in and draining only uplands and that do not carry a relatively permanent flow 

of water.” 2008 Guidance at 1, 12. The agencies’ proposed rule uses the term “ephemeral flow” 

rather than the term “non-relatively permanent flow” used in the 2008 Rapanos guidance 

because “ephemeral flow” is a commonly used technical and scientific term defined as flowing 

briefly in direct response to precipitation. The use of the term “ephemeral flow” will be clearer 

and therefore lead to more consistent jurisdictional determinations while reasonably identifying 

those ditches excavated wholly in and draining only uplands or non-jurisdictional wetlands or 

waters and have no more than ephemeral flow which should be excluded from the definition of 

“waters of the United States.” Note that the agencies consider ephemeral flows to be those with 

no identifiable groundwater contribution.

Only those ditches not excluded by the proposed regulation and that meet the proposed 

definition of tributary are waters of the United States. Ditches may be determined to be waters 

of the United States if they are wetlands and are adjacent to another water of the United States 

such as a traditional navigable water or a tributary. Ditches not excluded under paragraphs (b)(4) 

or (b)(5) of the proposed regulation meet the definition of tributary where they have a bed and 

banks and ordinary high water mark; they contribute flow directly or indirectly through other 

waterbodies to a traditional navigable water, interstate water, or the territorial seas. Non-tidal 
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ditches are waters of the United States in the proposed rule when they meet the definition of 

“tributary” and are any of the following:

• natural streams that have been altered (e.g., channelized, straightened or relocated);

• ditches that have been excavated in waters of the United States, including jurisdictional 

wetlands;

• ditches that have more than ephemeral flow; or

• ditches that connect two or more waters of the United States.

Under paragraphs (b)(4) and (b)(5), there are two categories of ditches that are not 

considered “waters of the United States” under the proposed rule: 

• Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow ; and

• Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

In an effort to clarify non-jurisdictional ditches from those that are “waters of the U.S.”, 

the proposal states that ditches with no more than ephemeral flow that are excavated in uplands, 

rather than in wetlands or other types of waters, for their entire length and that do not drain a 

jurisdictional wetland or other type of water are not tributaries and are not waters of the United 

States under the proposed rule. Similarly, ditches that do not drain into the tributary system of a 

traditional navigable water, interstate water or the territorial seas are not “waters of the United 

States,” even if, for example, the ditch has perennial flow. 

Historical evidence, such as historical photographs, prior delineations, or topographic 

maps, may be used to determine whether a waterbody was excavated wholly in uplands and 

drains only uplands or non-jurisdictional waters, and has no more than ephemeral flow. Site 
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characteristics may also be present to inform the determination of whether the waterbody is a 

ditch, such as shape, sinuosity, flow indications, etc. as, ditches are often created in a linear 

fashion with little sinuosity and may not connect to another “water of the U.S.” Ditches created 

by altering natural waters would be considered to be “waters of the U.S.”, so long as it 

contributes flow to another jurisdictional water. Ditches may have been created for a number of 

purposes, such as irrigation, water management or treatment, irrigation canals and roadside 

ditches and drains. In order to be non-jurisdictional, however, the ditch must still demonstrate 

that it was excavated wholly in uplands, drains only uplands or non-jurisdictional waters, and has 

no more than ephemeral flow, and/or does not contribute flow, either directly or through other 

waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this section. 

2. What is not a tributary for purposes of this proposal?

Waters that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of the regulation are not considered 

jurisdictional as tributaries under the CWA. However, they may be themselves (a)(1) or (a)(2) 

waters, or they may be jurisdictional if they fall under the “other waters” category (i.e., they have 

a significant nexus to an (a)(1) through (a)(3) water under (a)(7) of the proposed regulation). 

Note waters listed under the proposed (b), including ditches as defined under proposed (b)(4) and 

(b)(5), would not be considered waters of the United States in any case.

Section J below discusses in more detail the agencies proposed regulation excluding 

specific waters and features from the definition of waters of the United States. Of importance 

with respect to tributaries are the exclusion of gullies, rills, non-wetland swales, and certain 

ditches. These features are not considered tributaries under this proposed rule, even though rills 
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and gullies (as described in Section J), may contribute flow into a tributary in systems with steep 

side slopes.

Non-jurisdictional geographic features (e.g., non-wetland swales, ephemeral upland 

ditches) may still serve as a surface hydrologic connection between an adjacent wetland or water 

and a traditional navigable water, interstate water or a territorial sea, provided there is an actual 

exchange of water between those waterbodies, and the water is not lost to deep groundwater 

through infiltration (i.e., transmission losses). In addition, these geographic features may 

function as “point sources” (i.e., “discernible, confined and discrete conveyance[s]” under CWA 

section 502(14)), such that discharges of pollutants to waters through these features could be 

subject to other CWA authorities (e.g., CWA section 402 and its implementing regulations).

3. Why Do the Agencies Conclude All Tributaries Are “Waters of the United 

States”? 

Assertion of jurisdiction over tributaries as defined in this proposed rule is appropriate 

under Rapanos both as a legal matter and as a scientific matter based on available science and 

the agencies’ professional judgment and field expertise. The agencies conclude based on their 

scientific and technical expertise that tributaries, as defined in the proposed regulation, in a

watershed are similarly situated and have a significant nexus alone or in combination with other 

tributaries to the chemical, physical or biological integrity of traditional navigable waters, 

interstate waters or the territorial seas.

a. Legal Basis for Defining All Tributaries as Waters of the United States

In Rapanos, both the plurality opinion and Justice Kennedy’s opinion discussed the 

Court’s prior opinion in Riverside Bayview to begin their analysis of the scope of the CWA. 

Justice Scalia stated “In Riverside Bayview, we stated that the phrase [“waters of the United 
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States”] in the Act referred primarily to “rivers, streams, and other hydrographic features more 

conventionally identifiable as ‘waters’” than the wetlands adjacent to such features. 474 U. S., at 

131 (emphasis added).” Rapanos, 547 U.S. at 734. Justice Kennedy began, “As the plurality 

points out, and as Riverside Bayview holds, in enacting the Clean Water Act Congress intended 

to regulate at least some waters that are not navigable in the traditional sense.” Ante, at 12; 

Riverside Bayview, 474 U. S., at 133; see also SWANCC, supra, at 167. This conclusion is 

supported by “the evident breadth of congressional concern for protection of water quality and 

aquatic ecosystems.” Riverside Bayview, supra, at 133; see also Milwaukee v. Illinois, 451 U. S. 

304, 318 (1981) (describing the Act as “an all-encompassing program of water pollution 

regulation”). In Rapanos, Justice Kennedy established a standard for determining whether 

wetlands should be considered to possess the requisite nexus in the context of assessing whether 

wetlands are jurisdictional: “if the wetlands, either alone or in combination with similarly 

situated [wetlands] in the region, significantly affect the chemical, physical, and biological 

integrity of other covered waters more readily understood as ‘navigable.’” Id. at 780. While 

Justice Kennedy focused on adjacent wetlands in light of the facts of the cases before him, it is 

reasonable to utilize the same standard for tributaries. In addition, Justice Kennedy stated that 

“[t]hrough regulation or adjudication, the Corps may choose to identify categories of tributaries 

that, due to their volume of flow (either annually or on average), their proximity to navigable 

waters, or other relevant considerations, are significant enough that wetlands adjacent to them 

are likely, in the majority of cases, to perform important functions for an aquatic system 

incorporating navigable waters.” 547 U.S. at 780-81. As discussed in this preamble, based on a 

detailed examination of the scientific literature, the agencies conclude that tributaries as they 

propose to define them perform the requisite functions identified by Justice Kennedy for them to 
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be considered, as a category, to be waters of the United States. Assertion of jurisdiction over 

tributaries with a bed and banks and OHWM is also consistent with Rapanos because five 

Justices did not question the current regulations, which assert jurisdiction over non-navigable 

tributaries of traditional navigable waters and interstate waters.

The Report analyzes the scientific literature to determine whether tributaries to traditional 

navigable waters, interstate waters, or the territorial seas have a sufficient significant nexus to 

constitute “waters of the United States” under the Act such that it is reasonable to assert CWA 

jurisdiction over all such tributaries by rule, as a category. We provide an ecological rationale to 

demonstrate that tributaries draining to a traditional navigable water, interstate water, or the 

territorial seas have a significant nexus to such waters, especially because of their ability to 

transport pollutants to such waters that would impair their chemical, physical, and biological 

integrity.

One of the primary purposes and functions of the CWA is to prevent the dumping of 

petroleum wastes and other chemical wastes, biological and medical wastes, and all other forms 

of pollutants into the “waters of the United States,” because such pollutants endanger the 

nation’s public health, drinking water supplies, shellfish, fin fish, recreation areas, etc. Because 

the entire tributary system of the navigable and interstate waters is interconnected, pollutants that 

are dumped into any part of the tributary system eventually are washed downstream to navigable 

or interstate waters, where those pollutants endanger public health and the environment. The 

CWA regulates and controls pollution at its source, in part because most pollutants do not remain 

at the site of the discharge, but instead flow and are washed downstream through the tributary 

system to endanger drinking water supplies, fisheries, and recreation areas. These fundamental 

facts about the movement of pollutants and the interconnected nature of the tributary system 
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demonstrate why all tributaries of the traditional navigable waters and interstate waters have a 

significant nexus with those downstream waters. The significant nexus relating to pollution 

control between all tributaries of navigable and interstate waters and their downstream waters in 

and of itself justifies this rulemaking’s assertion of CWA jurisdiction by rule over all tributaries. 

b. The Agencies Conclude that Tributaries, as Defined in the 

Proposed Rule, Have a Significant Nexus

The finding of significant nexus is based on the chemical, physical, and biological

interrelationship between a water, the tributary network, and traditional navigable waters, 

interstate waters, and territorial seas. Based on their scientific and technical expertise, the 

agencies conclude that tributaries, as defined in today’s proposed rule, “are likely, in the majority 

of cases, to perform important functions for an aquatic system incorporating navigable waters.” 

Rapanos, 547 U.S. at 781-2. (For more discussion, see Appendix A). 

(1) Tributaries Significantly Affect the Physical Integrity of (a)(1) 

through (a)(3) Waters

Physical connections between tributaries and traditional navigable waters, interstate 

waters, and the territorial seas result from the hydrologic transport of numerous materials, 

including water, sediment and organic matter (e.g., leaves, wood) from tributaries to downstream 

waters. This transport affects the physical characteristics of downstream waters. Tributaries, even 

when seasonally dry, are the dominant source of water in most rivers, rather than direct 

precipitation or groundwater input to main stem river segments. 

One of the primary functions of tributaries is transporting sediment to downstream 

waters. Tributaries, particularly headwaters, shape and maintain river channels by accumulating 

and gradually or episodically releasing sediment and large woody debris into river channels. 
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Sediment transport is also provided by ephemeral streams. Effects of the releases of sediment 

and large woody debris are especially evident at tributary-river confluences, where 

discontinuities in flow regime and temperature demonstrate physical alteration of river structure 

and function by headwater streams. 

Tributaries have vitally important effects on the physical integrity of (a) (1) through (a) 

(3) waters, contributing not only the majority of the flow in these waters but affecting the 

structure of the waters. These effects occur even when the tributaries flow infrequently (such as 

ephemeral tributaries) and even when the tributaries are significant distances from the (a) (1) 

through (a) (3) water (such as some headwater tributaries). Tributaries provide flow to 

downstream rivers necessary to support navigation. The agencies conclude that these have a 

significant effect on the integrity of downstream waters.

(2) Tributaries Significantly Affect the Chemical Integrity of (a)(1)

through (a)(3) Waters

Tributaries also influence the chemical composition of downstream waters, through the 

transport of chemical elements and compounds, such as nutrients, ions, dissolved and particulate 

organic matter, pollutants, and contaminants. Ecosystem processes in tributaries transform, 

remove, and transport these substances to downstream waters. In turn, these chemical 

compounds can influence water quality, sediment deposition, nutrient availability, and biotic 

functions in rivers. Because water flow is the primary mechanism by which chemical substances 

are transported downstream, chemical effects are closely related to hydrological connectivity. 

Long-distance movement of contaminants provides another line of evidence for chemical 

connectivity between tributaries and traditional navigable waters, interstate waters or the 

territorial seas and significantly affect (a)(1), (a)(2) or (a)(3) waters. 
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Within tributaries, there are processes that occur that transform and export nutrients and 

carbon to downstream waters, serving important source functions that influence the chemical 

integrity of downstream waters. Organic carbon, in both dissolved and particulate forms, 

exported from tributaries is consumed by downstream organisms. The organic carbon that is 

exported downstream thus supports biological activity (including metabolism) throughout the 

river network. 

Tributaries have important effects on the chemical integrity of (a)(1) through (a)(3) 

waters, acting as both sinks and sources of chemical substances and have a large effect on the 

chemical integrity of the (a)(1) through (a)(3) waters. They provide sink functions by trapping 

chemicals through absorption to sediments in the stream substrate (e.g., phosphorous adsorption 

to clay particles). They provide source functions by transporting chemicals to downstream (a)(1) 

through (a)(3) waters as chemicals dissolved in the waters or as chemicals attached to suspended 

sediments. 

(3) Tributaries Significantly Affect the Biological Integrity of (a)(1)

through (a)(3) Waters

Tributaries, including intermittent and ephemeral streams, are critical in the life cycles of 

many organisms capable of moving throughout river networks. In fact, many organisms, such as 

anadromous salmon, have complex life cycles which involve migration through the river 

network, from headwaters to downstream rivers and oceans and back, over the course of their 

lives. Anadromous fish spend the majority of their life cycles in saltwater, but migrate upstream 

to inland freshwater systems in order to spawn and reproduce. In addition to providing critical 

habitat for complex life cycle completion, tributaries provide refuge from predators and adverse 

physical conditions in rivers and they are reservoirs of genetic- and species-level diversity. These 
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connections between tributaries and (a)(1) through (a)(3) waters influence the biologic integrity 

of these waters.

Tributaries have important effects on the biological integrity of (a)(1) through (a)(3) 

waters, contributing materials to downstream food networks and supporting populations for 

aquatic species, including economically important species such as salmon, etc., and other 

essential habitat needs for species that utilize both tributaries and downstream (a)(1) through 

(a)(3) waters. These effects occur even when the tributaries flow infrequently (such as ephemeral 

tributaries) and even when the tributaries are large distances from the (a)(1) through (a)(3) water 

(such as some headwater tributaries). 

(4) Tributaries Significantly Affect the Chemical, Physical, and 

Biological Integrity of (a)(1) through (a)(3) Waters 

As discussed above, the agencies conclude that tributaries, including headwaters, 

intermittent, and ephemeral streams, have a significant nexus to traditional navigable waters, 

interstate waters or the territorial seas based on their contribution to the chemical, physical, and 

biological integrity of (a)(1) through (a)(3) waters. Tributaries, including headwater streams, 

within a watershed draining to a traditional navigable water, interstate water, or the territorial 

seas collectively shape the chemical, physical, and biological integrity of (a)(1) through (a)(3) 

waters. 

Tributaries that are small, flow infrequently, or are a substantial distance from the nearest 

(a)(1) through (a)(3) water (e.g., headwater perennial, intermittent, and ephemeral tributaries) are 

essential components of the tributary network and have important effects on the chemical, 

physical, and biological integrity of (a)(1) through (a)(3) waters, contributing many of the same 

functions downstream as larger streams. When their functional contributions to the chemical, 
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physical, and biological conditions of downstream waters are considered at a watershed scale, 

the scientific evidence supports a legal determination that they meet the “significant nexus” 

standard articulated by Justice Kennedy in Rapanos. 

(5) Tributary Lakes, Ponds, and Wetlands Significantly Affect the 

Chemical, Physical, and Biological Integrity of (a)(1) through (a)(3) 

Waters

Although the above discussion refers primarily to stream tributaries, lake, pond and 

wetland tributaries also have the same or similar connections and functions that significantly 

affect (a)(1) through (a)(3) waters. Lakes and ponds that contribute surface water to downstream 

(a)(1) through (a)(3) waters satisfy the agencies’ definition of tributary. They may be at the 

headwaters of the tributary network (e.g. a lake with no stream inlets that has an outlet to the 

tributary network) or located outside of the headwaters, or farther downstream from the 

headwaters (e.g., a lake with both a stream inlet and a stream outlet to the tributary network). 

Similarly, wetland tributaries are wetlands that are located within the stream channel itself or that 

form the start of the stream channel, such as channel-origin wetlands that are part of the 

headwaters of the tributary network. 

Tributary lakes and ponds serve many important functions that affect the chemical, 

physical, and biological conditions downstream. Lakes can store floodwaters, sediment, and 

nutrients, as these materials have the opportunity to settle out, at least temporarily, as water 

moves through the lake downstream. Lakes, as with other tributaries, can also contribute flow, 

nutrients, sediment, and other materials downstream. 
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(6) Man-made or Man-altered Tributaries Significantly Affect the 

Chemical, Physical, and Biological Integrity of (a)(1) through (a)(3) 

Waters

Today’s proposal expressly states that a tributary, including wetlands, can be a natural, 

man-altered, or man-made water body and includes waters such as rivers, streams, lakes, 

impoundments, canals, and ditches not excluded from the definition of “waters of the United 

States” by paragraph (b) of the proposed rule. The agencies’ proposed rule clarifies that manmade and man-altered tributaries are waters of the United States because man-made and manaltered tributaries perform many of the same functions as natural tributaries, especially the 

conveyance of water that carries nutrients, pollutants, and other substances to traditional 

navigable waters, interstate waters, or the territorial seas. Man-made and man-altered tributaries 

also provide corridors for movement of organisms between headwaters and traditional navigable 

waters, interstate waters, or the territorial seas. The significant nexus between a tributary and a 

traditional navigable water or interstate water is not broken where the tributary flows through a 

culvert or other structure. The scientific literature recognizes that features that convey water, 

whether they are natural, man-made, or man-altered, provide the connectivity between streams 

and downstream rivers. 

Tributary ditches and other man-made or man-altered waters, if they meet the definition

of “tributary,” have a significant nexus to (a)(1) through (a)(3) waters due to their effects on the 

chemical, physical, or biological integrity of those downstream waters. As described above, 

tributaries of all flow regimes have a significant nexus to downstream (a)(1) through (a)(3) 

waters. Due to the often straightened and channelized nature of ditches, these tributaries quickly 

move water downstream to (a)(1) through (a)(3) waters. Ditches and canals, like other tributaries, 
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export sediment, nutrients, and other materials downstream. Due to their often channelized 

nature, ditches are very effective at transporting water and these materials, including nitrogen, 

downstream. It is the agencies’ position that ditches that meet the definition of tributary (and are 

not excluded under (b)(4) or (b)(5)) provide the same physical, chemical, and/or biological 

functions as other waterbodies defined as tributaries under the proposed rule.

IIIG. Adjacent Waters

The agencies propose to revise the existing jurisdictional category of “adjacent 

wetlands,” which currently limits consideration to only wetlands. The proposed “adjacent 

waters” category would replace “adjacent wetlands” and would include wetlands and other 

waterbodies that meet the proposed definition of adjacent, including “neighboring.” It would be 

necessary to determine that a wetland or other waterbody meets the definition of “adjacent”

water under proposed paragraph (a)(6) to establish jurisdiction. An adjacent water or wetland 

has a chemical, physical, and/or biological function that is integrally related to a regulated 

waterbody.

The proposed rule makes several changes to the existing rule. First, it proposes to change 

“adjacent wetlands” to “adjacent waters” so that waterbodies such as ponds and oxbow lakes, as 

well as wetlands, adjacent to jurisdictional waters are “waters of the United States” by 

regulation. Second, the proposed rule adds a definition of the term “neighboring,” which appears 

in the definition of “adjacent.” The agencies propose a definition for “neighboring” to identify 

those adjacent waters that the agencies concluded have a significant nexus to (a)(1) through 

(a)(3) waters. To bring greater clarity to the meaning of “neighboring,” the proposed rule adds 

two additional scientifically-based definitions for the terms “riparian area” and “floodplain” to 
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explain the lateral reach of the term “neighboring.” The proposed definitions of those two terms 

are set out below. The proposed rule reads in relevant part:

(a)(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) 

through (5) of this section; 

(c) Definitions

(1) Adjacent: The term adjacent means bordering, contiguous or 

neighboring. Waters, including wetlands, separated from other waters 

of the United States by man-made dikes or barriers, natural river berms, 

beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term 

“adjacent” in this section, includes waters located within the riparian 

area or floodplain of a water identified in paragraphs (a)(1) through 

(a)(5) of this section, or waters with a surface or shallow subsurface 

hydrologic connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a 

water where surface or subsurface hydrology influence the ecological 

processes and plant and animal community structure in that area. 

Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials 

between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or 

coastal waters that was formed by sediment deposition from such water 
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under present climatic conditions and is inundated during periods of 

moderate to high water flows.

1. What are “adjacent waters” under the proposed rule?

As explained in more detail below, “adjacent waters” are wetlands, ponds, lakes and 

similar water bodies that provide similar functions which, in concert with the functions provided 

by the tributaries to which they are adjacent, have a significant nexus to traditional navigable 

waters, interstate waters, and the territorial seas. In other words, tributaries and their adjacent 

waters function as a system that significantly affects the chemical, physical, and biological 

integrity of traditional navigable waters, interstate waters, and the territorial seas. This also 

includes waters and wetlands that are themselves adjacent to traditional navigable waters, 

interstate waters, and the territorial seas. The inclusion of adjacent waters in this category is 

supported by the Report, the collective body of scientific literature, the agencies’ growing body 

of scientific and technical knowledge and practical expertise addressing the connectivity and 

ecological interactions of these waters on downstream (a)(1) through (a)(3) waters, and by the 

determination made in this rulemaking that, in the aggregate, all adjacent waters have a 

significant nexus with their downstream traditional navigable waters or interstate waters.

Under the existing rule, only wetlands adjacent to “waters of the United States” are 

defined as “waters of the United States.” As noted in San Francisco Baykeeper v. Cargill Salt, 

481 F.3d 700 (9th Cir. 2007), this provision of the agencies’ regulations only defines adjacent 

wetlands, not adjacent ponds, as waters of the United States. Prior to SWANCC, adjacent nonwetland waters were often found jurisdictional under the “other waters,” or “(a)(3)” provision of 

the existing regulations. Waters, including wetlands, that meet the proposed definition of 

adjacency, including the new proposed definition of neighboring, have a significant nexus to 
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(a)(1) through (a)(3) waters, and under this proposed rule would include all adjacent waters,

including wetlands, as “waters of the United States” by rule. 

The existing definition of “adjacent” would be generally retained under today’s proposal, 

with a clarification. The proposed rule states: “[t]he term adjacent means bordering, contiguous 

or neighboring. Waters, including wetlands, separated from other waters of the United States by 

man-made dikes or barriers, natural river berms, beach dunes and the like are ‘adjacent waters.’” 

The rule also proposes for the first time a definition of the term “neighboring.’ Even if 

bordering, contiguous or neighboring waters are separated from an (a)(1) through (a)(5) water by 

natural or man-made features such as berms or other barriers or the like, the waters are 

“adjacent” and thus “waters of the United States” under proposed paragraph (a)(6). Within the 

definition of “adjacent,” the terms bordering and contiguous are well understood, and for 

continuity and clarity the agencies would continue to interpret and implement those terms 

consistent with existing policy and practice. Note that the lateral limits of an adjacent water, 

other than wetlands or tributaries, is determined by the presence of an OHWM without the need 

for a bed and banks. (33 CFR Section 328.3(e)).

The term “neighboring” has generally been interpreted broadly. The agencies provide a 

regulatory definition of “neighboring” that captures those waters that in practice the agencies 

have identified as having a significant effect on the chemical, physical and biological integrity of 

traditional navigable waters, interstate waters or the territorial seas. “Neighboring” is defined as 

including, “waters located within the riparian area or floodplain of a water identified in 

paragraphs (a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface 

hydrologic connection to such a jurisdictional water.” The terms “riparian area” and 
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“floodplain” are also defined to further clarify how we interpret the term “neighboring.” Those 

new terms are found at subsection (c)(1) through (c)(4) of the proposed rule.

Under the proposed definition for “neighboring,” waters, including wetlands, that are 

located within the riparian area or floodplain of an (a)(1) through (a)(5) water would be 

jurisdictional without a case-specific significant nexus analysis. Most waters, including 

wetlands, that are bordering or contiguous to a waterbody are found within its riparian zone or 

floodplain. However, there are some bordering or contiguous waters that might be located 

outside of the riparian zone or floodplain, such as wetlands immediately next to a highly incised 

and manipulated stream that no longer has a riparian area or a floodplain. Waters, including 

wetlands, determined to have a surface or shallow subsurface hydrologic connection to an (a)(1) 

through (a)(5) water would also be waters of the United States by definition. In circumstances 

where a particular waterbody is outside of the floodplain and riparian area of a tributary, but is 

connected by surface or shallow subsurface hydrology with such tributary, the agencies will also 

assess the distance between the waterbody and tributary in determining whether or not the 

waterbody is adjacent. The scientific literature, supplemented by agency practice, leads to a 

recognition of the role of hydrologic connections in supporting a substantial chemical, physical, 

and biological relationship between waterbodies, but this relationship can be reduced as the 

distance between waterbodies increases. The agencies recognize that in specific circumstances, 

the distance between waterbodies may be sufficiently far that even the presence of a hydrologic 

connection may not support an adjacency determination.

Both surface and shallow subsurface connections are forms of direct hydrologic 

connections between adjacent waters and (a)(1) through (a)(5) waters. Examples of surface 

connections would include small conveyances, swales or non-jurisdictional ditches, such as the 
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two categories listed in paragraph (b)(3), that connect the two water bodies. A shallow 

subsurface hydrologic connection is lateral water flow through a shallow subsurface layer, such 

as can be found in steeply sloping forested areas with shallow soils, or soils with a restrictive 

horizon that impedes the vertical flow of water or, in karst systems, especially karst pans. A 

shallow subsurface connection also exists, for example, when the adjacent water and neighboring 

(a)(1) through (a)(5) water are in contact with the same shallow aquifer. These connections 

would provide evidence of a water body being adjacent, even if those connections would not be 

considered “waters of the United States” in and of themselves.

Application of the terms “riparian area,” “floodplain,” and “hydrologic connection”

would be based in part on best professional judgment and experience applied to the definitions 

contained in this rule. The new definitions of riparian area and floodplain are designed to 

provide greater consistency, clarity, and certainty in determining the circumstances where the 

proximity and location of a particular water meet the term adjacent. The addition of these two 

terms is based on the scientific literature and agencies’ knowledge of and expertise on river 

systems, which shows that water bodies such as wetlands, ponds, and oxbow lakes located within 

the riparian areas and floodplains of (a)(1) through (a)(5) waters generally have substantial 

hydrologic and ecologic connections with the waters that they neighbor. These proposed 

definitions are adapted from scientific definitions using the concepts that are most relevant and 

useful in the context of the CWA. See, e.g., Id. When determining whether a water is located in 

a floodplain, the agencies will use best professional judgment to determine which flood interval 

to use (for example, 10 to 20 year flood interval zone).

Finally, the agencies are also proposing to delete the parenthetical from the existing 

“adjacent wetlands” regulatory provision: “Wetlands adjacent to waters (other than waters that 
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are themselves wetlands) identified in paragraphs (a) through (f) of this definition.” The phrase 

“other than waters that are themselves wetlands” was intended to preclude asserting CWA

jurisdiction over wetlands that were simply adjacent to another wetland (such as an “isolated”

wetland, as opposed to a wetland adjacent to a tributary). However, in practice some wetlands 

that were indeed adjacent to a tributary were found to not meet the definition of “adjacent” 

simply because another adjacent wetland was located between the adjacent wetland and the 

tributary. With this proposed change, the agencies intend to ensure that all waters that meet the 

proposed definition of “adjacent” are “waters of the United States,” regardless of whether or not 

another adjacent water is located between those waters and the tributary. If, for example, one 

wetland is in the riparian area of a “tributary” as defined in today’s proposed rule, and a different 

wetland is in the floodplain of that tributary, both wetlands would meet the definition of 

“adjacent” and be “waters of the United States,” even if the riparian wetland is located between 

the floodplain wetland and the tributary. Each wetland’s jurisdictional status in this example is 

based on a case-specific determination of whether it meets the definition of “adjacent.” Waters 

located near an adjacent water but which are not themselves (independently) adjacent to a 

tributary would, under the proposed rule, not be regulated under (a) (6). However, waters, 

including wetlands, that are adjacent to a wetland that meets the definition of a tributary would 

be considered adjacent waters.

2. Why do the agencies conclude that adjacent waters are waters of the United 

States?

a. Legal Basis for Defining All Adjacent Waters as Waters of the United 

States
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For those wetlands adjacent to (a)(1) through (a)(3) waters, Justice Kennedy stated in 

Rapanos that the agencies’ existing regulation “rests upon a reasonable inference of ecologic 

interconnection, and the assertion of jurisdiction for those wetlands is sustainable under the Act 

by showing adjacency alone.” 547 U.S. at 780. For all other adjacent waters, including adjacent 

wetlands, Justice Kennedy has provided a framework for establishing categories of waters which 

are per se “waters of the United States.” First, he provided that wetlands are jurisdictional if 

they “either alone or in combination with similarly situated lands in the region, significantly 

affect the chemical, physical, and biological integrity of other covered waters more readily 

understood as ‘navigable.’” 547 U.S. at 780. While the issue was not before the Supreme Court, 

it is reasonable to also assess whether non-wetland waters have a significant nexus, as Justice 

Kennedy’s opinion makes clear that a significant nexus is the touchstone for CWA jurisdiction. 

Justice Kennedy also provided that the agencies could through regulation or adjudication identify 

categories of waters that “are likely, in the majority of cases, to perform important functions for 

an aquatic system incorporating navigable waters.” 547 U.S. at 780-81. 

Adjacent waters as defined in today’s proposed rule, alone or in combination with other 

adjacent waters in a watershed that drains to a traditional navigable water, interstate water or the 

territorial seas, do significantly affect the chemical, physical and biological integrity of those 

waters. Waters that are adjacent to (a)(1) through (a)(5) waters, including wetlands, oxbow lakes 

and adjacent ponds, are integral parts of stream networks because of their ecological functions 

and how they interact with each other, and with downstream traditional navigable waters, 

interstate waters, or the territorial seas. In other words, tributaries and their adjacent waters, and 

the downstream traditional navigable waters, interstate waters, and territorial seas in which those 

waters flow into, are an integrated ecological system, and discharges of pollutants, including 
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discharges of dredged or fill material, into these components of that ecological system, must be 

regulated under the CWA to restore and maintain the chemical, physical, or biological integrity 

of these waters.

The agencies’ proposed regulation is consistent with the statute, the Supreme Court’s 

decisions, the best available science, and scientific and technical expertise, see both Appendices 

A and B. 

b. Adjacent waters under this proposed rule have a significant nexus to 

downstream (a)(1) through (a)(3) waters.

The agencies’ proposal to determine “adjacent waters” jurisdictional is supported by the 

substantial chemical, physical, and biological relationship between adjacent waters, alone or in 

combination with similarly situated waters, and (a)(1) through (a)(5) waters. Adjacent wetlands 

and other adjacent waters such as ponds and oxbow lakes perform important functions for the

nearby streams and lakes, and these functions are significant for the chemical, physical, and 

biological integrity of adjacent and downstream waters. See Appendix A. 

One reason why the EPA and the Corps determined in this rulemaking that all adjacent 

waters have a significant nexus with their downstream navigable or interstate waters is closely 

related to a primary reason (explained above) why all tributaries of navigable and interstate 

waters have a significant nexus with those downstream waters. That is, all adjacent waters 

should be jurisdictional by rule because the discharge of many pollutants (such as petroleum 

wastes and other toxic pollutants) discharged into adjacent waters often would flow downstream 

into and thereby pollute the navigable or interstate waters.

Based on science and agency expertise, the agencies concluded that adjacent waters, as 

defined in the proposed rule, “are likely, in the majority of cases, to perform important functions 
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for an aquatic system incorporating navigable waters.” Rapanos, 547 U.S. at 781-82 The 

agencies identified the characteristics of adjacent waters that as a class have a significant nexus 

to (a)(1) through (a)(3) waters: they are waters that are bordering to or are contiguous with (a)(1) 

through (a)(5) waters, including wetlands; they are waters that lie within the riparian area or 

floodplain of a (a)(1) through (a)(5) waters; or they are waters that have a surface or shallow 

subsurface connection with such (a)(1) through (a)(5) waters. These characteristics ensure that 

the adjacent waters are part of “an aquatic system incorporating navigable waters,” 547 U.S. at 

781-82; and that they perform important functions to maintain the chemical, physical, or 

biological integrity of an (a)(1) through (a)(3) water. 

In showing chemical, biological, and physical connections between adjacent waters and 

other jurisdictional waters, adjacent waters, including wetlands, may be separated by land or 

other features not regulated under the CWA, but those intervening uplands do not eliminate or 

impede the functional interactions between (a)(1) through (a)(5) waters and the waters, including 

wetlands, that are adjacent to them. For instance, two waters may be separated by upland but be 

connected through surface or shallow subsurface connections with water and chemicals readily 

exchanging between them. Similarly, uplands separating two waters may not act as a barrier to 

animals that regularly move between the two waters. Therefore, this proposed rule reflects an 

understanding that adjacent waters affect the chemical, physical, and biological integrity of 

waters to which they are adjacent and to (a)(1) through (a)(3) waters even where the two waters 

may be separated by features that are not jurisdictional, such as uplands, berms, roads, levees, 

and similar features. The presence of these features does not extinguish jurisdiction, a 

conclusion contained in the agencies’ existing regulation at 33 CFR 328.3 (c).
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(1) Riparian and Floodplain Waters Significantly Affect the Chemical, Physical, and 

Biological Integrity of (a)(1) through (a)(3) Waters

Riparian and floodplain waters, including wetlands, that are adjacent to (a)(1) through 

(a)(3) waters play an integral role in maintaining the chemical, physical, and biological integrity 

of those waters. In addition, riparian and floodplain waters, including wetlands, that are adjacent 

to (a)(4) and (a)(5) waters and those (a)(4) and (a)(5) waters themselves, should be considered 

together as a functional ecosystem, and as such provide an important role in maintaining the 

chemical, physical, and biological integrity of traditional navigable waters, interstate waters, or 

the territorial seas. Riparian areas are often located within the floodplains of waterbodies. 

(2) Waters, Including Wetlands, Determined to Have a Surface or Shallow

Subsurface Hydrologic Connections Significantly Affect the Chemical, Physical, 

and Biological Integrity of (a)(1) through (a)(3) Waters.

The proposed rule includes as adjacent those waters that are “neighboring” because they 

possess a surface or shallow subsurface hydrologic connection to a jurisdictional water, and 

therefore can exchange water, along with chemicals and organisms within that water, with an 

(a)(1) through (a)(5) water, and subsequently have a significant effect on the chemical, physical, 

and biological integrity of a downstream traditional navigable water, interstate water, or 

territorial sea. Surface connections that provide a pathway for water to be exchanged between 

the potentially adjacent wetland or water, and an (a)(1) through (a)(5) water present the clearest 

evidence of a hydrologic connection. Shallow subsurface connections are equally important, yet 

are more difficult to identify and document. Relevant evidence shows that waters, including 

wetlands, located outside of the riparian area or flood plain, but which still have a surface or 

shallow subsurface hydrologic connection to an (a)(1) through (a)(5) water, will have a 
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significant nexus to downstream (a)(1) through (a)(3) waters. Note that nothing under this 

proposed rule would cause the shallow subsurface connections themselves to become

jurisdictional.

Examples of surface water hydrologic connections are swales, gullies, or rills. The

frequency, duration, and volume of flow associated with these connections can vary greatly

depending largely on factors such as precipitation, snowmelt, landforms, soil types, and water 

table elevation. It is the presence of this hydrologic connection which provides the opportunity 

for neighboring waters to influence the chemical, physical, or biological integrity of (a)(1) 

through (a)(5) waters.

In circumstances where a particular water is outside of the floodplain and riparian area of 

a jurisdictional waterbody, a connection can be established by surface or shallow subsurface 

hydrology that makes the water neighboring, and thus adjacent. The scientific literature 

recognizes the role of hydrologic connections in supporting a substantial chemical, physical, and 

biological relationship between waterbodies, but this relationship can be reduced as the distance 

between waterbodies increases because of various factors, such as soil characteristics, geology, 

climate, precipitation patterns, etc. The distance between waterbodies may be sufficiently great 

that even the presence of an apparent hydrologic connection may not support an adjacency 

determination. The greater the distance, the less likelihood that there is an actual surface or 

shallow subsurface hydrologic connection, because of the greater potential for the water to 

infiltrate the soil to deeper groundwater, or for transmission losses in any gully or swale (for 

example) that may appear to be hydrologic connections. A determination of adjacency based on 

surface or shallow subsurface hydrologic connection outside the riparian area or floodplain 

requires clear documentation. 
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IIIH. “Other Waters”

The “other waters” section of the proposed regulation is at (a)(7), and provides that “On a 

case-specific basis, other waters, including wetlands, provided that the water alone, or in 

combination with other similarly situated waters located in the same region, has a significant 

nexus to a water identified in paragraphs (1) through (3) of this section.” To be clear, these 

“other waters” are not jurisdictional as a single category; rather, as the proposed rule language 

states, “ other waters” are jurisdictional provided that they are found, on a case-specific basis, to 

have a significant nexus to an (a)(1) through (a)(3) water. Thus, the introductory phrase “on a 

case-specific basis” is designed to signal clearly that this provision of the definition of “waters of 

the United States” does not mean “other waters” are waters of the United States by definition, in 

contrast to those defined in proposed paragraphs (a)(1) through (a)(6). “Other waters” will be 

evaluated individually or as a group of waters in a single landscape unit if they are located 

sufficiently close together or close to a jurisdictional water. How these “other waters” are 

aggregated for a case-specific significant nexus analysis depends on their spatial arrangement 

within the “region” or watershed. “Other waters” generally have similar functions, so it is the 

landscape position within the watershed (i.e., the “region”) that is the determinative factor for the 

significant nexus analysis, which will focus on the degree to which the functions provided by 

those “other waters” affect the chemical, physical, or biological integrity of (a)(1) through (a)(3) 

waters. 

Significant nexus is then proposed to be defined at (c)(7) of the regulations and provides 

that “The term significant nexus means a more than speculative or insubstantial effect that a 

water (including wetlands), either alone or in combination with other similarly situated waters in 
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the region (i.e., the watershed that drains to a water identified in paragraphs (a)(1) through (3) of 

this section), on the chemical, physical or biological integrity of a water identified in paragraphs 

(a)(1) through (3) of this section. “Other waters” (including wetlands) are similarly situated 

when they perform similar functions and are located sufficiently close together or close to a 

“water of the U.S.” so that they can be evaluated as a single landscape unit with regard to their 

effect on the physical, chemical, or biological integrity of a water identified in paragraphs (a)(1) 

through (a)(3) of this section.” Together, these two provisions allow for the possibility of 

establishing jurisdiction over waters that do not fit within the definition of another of the 

proposed categories of waters of the United States and are not excluded from the definition of 

waters of the United Stated under proposed (b). 

The proposed regulation also provides the agencies’ interpretation of significant nexus. 

Accordingly, a significant nexus analysis may be based on a particular water alone or based on 

the effect that the water has in combination with other similarly situated waters in the region. 

The agencies are proposing to interpret the region to identify similarly situated waters as the 

watershed that drains to a water identified in paragraphs (a)(1) through (a)(3). For purposes of 

analyzing whether an “other water” has a significant nexus, the agencies are proposing that 

“other waters” are similarly situated if they perform similar functions and they are either (1) 

located sufficiently close together so that they can be evaluated as a single landscape unit with 

regard to their effect on the chemical, physical, or biological integrity of a water identified in 

paragraphs (a)(1) through (a)(3), or (2) located sufficiently close to a “water of the U.S.” for such 

an evaluation of their effect. These criteria are explained in a subsequent section.

Consistent with Justice Kennedy’s opinion in Rapanos, the agencies propose today to

establish a case-specific analysis of whether “other waters,” including wetlands, that do not meet 
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the criteria for any of the proposed jurisdictional categories in (a)(1) through (a)(6) and are not 

proposed to be excluded by rule under paragraph (b) of the rule, have a significant nexus to a 

traditional navigable water, an interstate water or the territorial seas, and therefore, are waters of 

the United States. The agencies specifically considered whether sufficient information existed 

about certain subcategories of “other waters” to support a conclusion that the particular waters, 

alone or in combination, had a significant nexus to waters identified in paragraphs (a)(1) through 

(a)(3), but concluded that there is not sufficient scientific information or practical knowledge at 

this time to support establishing such subcategories of “other waters” as jurisdictional per se, 

Therefore, at this time the agencies are not proposing to identify any other category or categories 

of waters over which to assert jurisdiction. 

1. Significant Nexus Analysis for “Other Waters” 

a. “Other Waters”

As noted earlier, “other waters” are those waters, including wetlands, that do not meet the 

criteria of any of the categories of waters in (a)(1) through (a)(6) and also are not one of the 

features excluded from the definition of waters of the United States, and thus are subject to a 

case specific significant nexus determination. In the existing regulation, there is a non-exclusive 

list of the types of “other waters” which may be found to be waters of the United States: “All 

other waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, 

sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds.” The 

agencies are not proposing to re-promulgate this list of “other waters” because the list does not 

seem necessary and because it could cause confusion because some have read it as an exclusive 

list. Of more concern was that the existing descriptive list of types of “other waters” includes 

some waters that would be jurisdictional under one of the proposed categories of waters of the 
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United States that would be jurisdictional by rule. The agencies want to be clear, for example,

that an intermittent stream that meets the definition of tributary does not also need a separate 

significant nexus analysis. By removing that list of water types for clarity, the agencies do not 

intend to imply that any of the waters listed in the existing regulation are not jurisdictional. 

When one of the waters on the enumerated list does not fall under another proposed category (for 

example, adjacent waters under (a)(6) or tributaries under (a)(5)), those waters would be

jurisdictional if found to have a significant nexus under this proposed section on a case-specific 

basis.

b. Significant Nexus

The agencies recognize that Supreme Court decisions in SWANCC and Rapanos 

identified limitations on the geographic scope of “other waters” that may be determined to be 

jurisdictional. Therefore, the agencies’ proposal today provides that waters not covered by any 

other regulatory category are jurisdictional only if they are determined on a case-specific basis to 

have a significant nexus to a traditional navigable water, an interstate water, or the territorial 

seas. 

Justice Kennedy explained the SWANCC decision in his concurring opinion in Rapanos: 

“In Solid Waste Agency of Northern Cook Cty. v. Army Corps of Engineers, 531 U.S. 159 (2001) 

(SWANCC), the Court held, under the circumstances presented there, that to constitute ‘navigable 

waters’ under the Act, a water or wetland must possess a ‘significant nexus’ to waters that are or 

were navigable in fact or that could reasonably be so made.” 547 U.S. at 759. Since the Court in 

SWANCC was considering the validity of the Corps’ assertion of jurisdiction over ponds and 

mudflats under (a)(3) of the existing Corps’ regulations (33 CFR 328.3), the agencies interpret 

the significant nexus standard to apply to the “other waters” of the existing regulation.
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The “other waters” or “(a)(3) waters” provision of EPA’s and the Corps existing 

regulations includes: 

“All other waters such as intrastate lakes, rivers, streams (including intermittent streams), 

mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or 

natural ponds, the use, degradation or destruction of which could affect interstate or 

foreign commerce ....”

To comport with the SWANCC and Rapanos decisions, the agencies are proposing to 

delete the requirement that an “other water” be one “the use, degradation or destruction of which 

could affect interstate or foreign commerce” and to replace it with the requirement that the “other 

water” meet Justice Kennedy’s significant nexus standard. The current regulations assert 

jurisdiction more broadly than what is proposed today. With this proposed regulation, the 

agencies are limiting regulation of “other waters” to only those that are determined on a casespecific basis to have a significant nexus to an (a)(1) through (a)(3) water. For the purpose of 

assessing whether an “other water” has a significant nexus, the agencies are also proposing a 

definition of significant nexus. See Appendix B, Legal Analysis.

For purposes of assessing whether a particular water is a water of the United States 

because it, alone or in combination with other similarly situated waters, has a significant nexus to 

an (a)(1) through (a)(3) water, the agencies are proposing to define each of the elements of the 

significant nexus standard in the definition of “significant nexus.”

i. In the Region

The agencies propose to interpret the phrase “in the region” to mean the watershed that 

drains into the nearest traditional navigable water, interstate water or the territorial seas through a 

single point of entry. That concept is established in the definition of “significant nexus” at 
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(c)(7): “. . . in the region (i.e., the watershed that drains to a water identified in paragraphs (a)(1) 

through (3) of this section) . . .” Justice Kennedy did not define the “region.” The agencies 

determined that because the movement of water from watershed drainage basins to river 

networks and lakes shapes the development and function of these systems in a way that is critical 

to their long term health, the watershed is a reasonable and technically appropriate scale on 

which to identify waters that together may have an effect on the physical, chemical or biological 

integrity of a particular (a)(1), (a)(2) or (a)(3) water, consistent with Justice Kennedy’s standard. 

See Appendix A, Scientific Analysis. 

The point of entry watershed is the drainage basin within whose boundaries all 

precipitation ultimately flows to a single traditional navigable water. The watershed includes all 

lands, streams, wetlands, lakes, and other waters within its boundaries.

In light of the scientific literature, the longstanding approach of the agencies to 

implementation of the CWA, and the statutory goals underpinning Justice Kennedy’s significant 

nexus framework, the watershed draining to an (a)(1) through (a)(3) water is the appropriate 

“region” for a significant nexus analysis.

ii. Similarly Situated 

The agencies’ proposed regulation would apply Justice Kennedy’s significant nexus test 

in determining whether “other waters” are waters of the United States. The “other waters” 

section of the proposed regulation is at (a)(7), and provides that such waters, including wetlands, 

are waters of the United States when “[o]n a case-specific basis, other waters, including 

wetlands, provided that the water alone, or in combination with other similarly situated waters 

located in the same region, has a significant nexus to a water identified in paragraphs (a)(1) 

through (a)(3) of this section.” The proposed regulation at (c)(7) further clarifies that “other 
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waters, including wetlands, are similarly situated when they perform similar functions and are 

located sufficiently close together or close to a water of the United States so that they can be 

evaluated as a single landscape unit with regard to their effect on the chemical, physical, or 

biological integrity of a water identified in paragraphs (a)(1) through (a)(3) of this section” (i.e., 

traditional navigable waters, interstate waters or the territorial seas). This portion of the 

regulation allows for determining jurisdiction over waters that are not contained within the 

definition of another of the proposed categories of waters of the United States and are not 

excluded from the definition of waters of the United States under (b).

Justice Kennedy provided guidance to the agencies that establishing a significant nexus 

requires examining whether a water “alone or in combination with similarly situated [waters] in 

the region, significantly affect[s] the chemical, physical, and biological integrity of other covered 

waters more readily understood as ‘navigable.’” 547 U.S. at 780. The proposed rule adopts the 

concept of aggregating certain waters to determine whether such waters meet the “alone or in 

combination with similarly situated waters” test. 

The proposed rule requires that waters perform similar functions and be located 

sufficiently close together or close to a water of the U.S so that they can be evaluated as a single 

landscape unit with regard to their effects. This combination of functionality and proximity to 

each other or to a water of the United States meets the guidance provided by Justice Kennedy. 

Examining both functionality and proximity also limits the “other waters” that can be aggregated 

for purposes of determining jurisdiction. The science contained in the Report supports a 

conclusion that there is insufficient information at this time to determine that entire categories of 

“other waters” should be determined to be jurisdictional by rule. This is in contrast to the 
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conclusion in the proposed rule that tributaries possess the requisite significant nexus to be 

determined jurisdictional as a category. 

It is appropriate to analyze the chemical, physical, or biological effects “other waters” 

perform individually or together with all similarly situated “other waters” in the same region. 

Today, the agencies are proposing to identify factors to apply in the determination of when 

“other waters” should be considered either individually or as a single landscape unit for purposes 

of a significant nexus analysis. The agencies’ proposed rule defines “similarly situated” “other 

waters” as waters that perform similar functions and are located in the landscape either 

sufficiently close to each other or close to a water of the United States that it is appropriate to 

consider their combined effects on the chemical, physical, or biological integrity of a traditional 

navigable water, interstate water, or territorial sea. The agencies recognize not all “other waters”

within the region should be considered similarly situated for the purposes of assessing whether a 

significant nexus exists. As a result, the agencies propose to define “similarly situated” to 

require an evaluation of either a single water or group of waters (i.e., a single landscape unit) in 

the region that can reasonably be expected to function together in their effect on the chemical, 

physical, or biological integrity of downstream traditional navigable waters, interstate waters or 

territorial seas.

In addition, the agencies propose that “other waters” located close to a jurisdictional 

water are more likely to influence such waters and therefore, to affect the integrity of 

downstream (a)(1) through (a)(3) waters. These “other waters,” which do not meet the proposed 

definition of adjacent waters, may be assessed together when determining on a case-specific 

basis whether a significant nexus exists, because of their similar functions and similar location in 

the landscape.
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Agencies will conduct case-specific analyses of “other waters” at the project site and 

within the single point of entry watershed in which these “other waters” are located to determine 

whether a significant nexus exists between these “other waters” and the nearest (a)(1) through 

(a)(3) water. “Other waters,” including wetlands, are similarly situated when they perform 

similar functions and are located sufficiently close together or close to a “water of the U.S.” so 

that they can be evaluated as a single landscape unit within that watershed. Similarly situated

waters may be identified as sufficiently close together for purposes of this section of the 

proposed regulation when they are within a contiguous area of land with relatively homogeneous 

soils, vegetation and landform (e.g., plain, mountain, valley, etc.). As a general matter, it would 

be inappropriate, for example, to consider “other waters” as “similarly situated” if these “other 

waters” are located in different landforms, have different elevation profiles, or have different soil 

and vegetation characteristics, unless the “other waters” are located similarly near a “water of the 

U.S.,” which may allow such “other waters” to more consistently and collectively function to 

effect an (a)(1) through (a)(3) water. However, the agencies may also consider: the hydrologic 

and ecological bases for establishing a grouping as a single landscape unit; the geographic 

distribution of these “other waters;” the distance between these waterbodies and their proximity 

to jurisdictional waters within the watershed; the functions performed by the “other waters,” such 

as habitat, water storage, sediment retention, and pollution sequestration; and hydrologic 

connectivity with jurisdictional waters. These and other relevant considerations should be used 

by the agencies to document the hydrologic, geomorphic and ecological characteristics and 

circumstances. Examples include: documentation of physical, chemical and biological 

interactions of the similarly situated “other waters”; aerial photography; topographical or terrain 

maps and information; other available GIS data; National Wetland Inventory Maps; and state and 
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local information. The evaluation should use any available site information and pertinent field 

observations where available, relevant scientific studies or data, or other relevant jurisdictional 

determinations that have been completed in the region. The agencies generally use available 

mapping tools that are based on the National Hydrography Dataset (NHD) to demarcate 

boundaries of the single point of entry watershed. This point of entry approach identifies a group 

of waters that flow to a single location and represents the scientifically appropriate sized area for 

conducting a significant nexus evaluation in most cases. In the arid West, the agencies recognize 

there may be situations where the single point of entry watershed is very large, and it may be 

resource intensive to demarcate watershed boundaries and all relevant waters in the watershed. 

Under those circumstances, for practical administrative purposes the agencies could use the 

NHD mapping tool to demarcate catchments surrounding the water to be evaluated that, in 

combination, are roughly the size of the typical nearby 10-digit hydrologic unit code (HUC-10)

watershed. This combination of catchments would be used for conducting a significant nexus 

evaluation. Such an approach can help resolve some practical concerns of using available 

mapping tools on very large single point of entry watersheds in the arid West. Under the 

proposed rule, the agencies would assess the combined effects of similarly situated “other 

waters” in the same region on the chemical, physical, or biological integrity of (a)(1), (a)(2) and 

(a)(3) waters in conducting a significant nexus analysis. The factors identified above would be 

used by the agencies in determining “other waters” in the region that are similarly situated and 

should, therefore, be considered together in conducting a significant nexus analysis. 

The agencies identified a number of factors relevant to determining whether “other 

waters” are similarly situated for conducting a significant nexus analysis. However, the agencies 

recognize that consideration of these factors will often limit aggregation of “other waters” for 
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purposes of assessing significant nexus or will require that “other waters” be considered 

individually with no aggregation. The agencies request public comment on this approach and 

whether alternative approaches may be more consistent with the best available science and 

Justice Kennedy’s opinion in Rapanos.

iii. Significant Nexus

The agencies propose to define the term “significant nexus” consistent with language in 

SWANCC and Rapanos. The proposed definition of “significant nexus” at (c)(7) relies most 

importantly on Justice Kennedy’s Rapanos opinion, which recognizes that not all waters have 

this requisite connection to waters covered by paragraphs (a)(1) through (a)(3) of the proposed 

regulations. Justice Kennedy was clear that the requisite nexus must be more than “speculative 

or insubstantial,” Rapanos, at 780, in order to be significant and the agencies propose to define 

significant nexus in precisely those terms. It is important to note that in Rapanos, Justice 

Kennedy did not conclude that the wetlands adjacent to ditches in the cases before the Court 

were not waters of the United States. Rather, Justice Kennedy concluded that the proper inquiry 

to determine their jurisdictional status - whether or not the wetlands had a “significant nexus” -

had not been made by the Corps or the courts below. In fact, Justice Kennedy stated that in both 

the consolidated cases before the Court the record contained the types of evidence relevant to 

the determination of a significant nexus according to the principles he identified. Justice 

Kennedy stated “[m]uch the same evidence should permit the establishment of a significant 

nexus with navigable-in-fact waters, particularly if supplemented by further evidence about the 

significance of the tributaries to which the wetlands are connected.” Id. Thus, Justice Kennedy 

concluded that “the end result in these cases and many others to be considered by the Corps may 
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be the same as that suggested by the dissent, namely, that the Corps’ assertion of jurisdiction is 

valid.” See Appendix B, Legal Analysis.

The agencies will determine whether the water they are evaluating, in combination with 

other similarly situated waters in the watershed, has a significant nexus to the nearest traditional 

navigable water or interstate water. Functions of waters that might demonstrate a significant 

nexus include sediment trapping, nutrient recycling, pollutant trapping and filtering, retention or 

attenuation of flood waters, runoff storage, and provision of aquatic habitat. A hydrologic 

connection is not necessary to establish a significant nexus, because in some cases the lack of a 

hydrologic connection would be a sign of the water’s function in relationship to the traditional 

navigable water or interstate water, such as retention of flood waters or pollutants that would 

otherwise flow downstream to the traditional navigable water or interstate water.

I. Waters that are not Waters of the United States

The agencies’ longstanding regulations exclude waste treatment systems designed to 

meet the requirements of the CWA and prior converted cropland from the definition of waters of 

the United States. The agencies propose no changes to these exclusions and therefore they are 

restated as a part of this rulemaking. The agencies also propose to codify longstanding practices

that have generally considered certain features and types of waters not to be waters of the United 

States. Under today’s proposal, the waters identified in the regulation would clearly not be 

waters of the United States. 

The agencies propose to take some ministerial actions with respect to the placement of 

the two existing exemptions for waste treatment systems and prior converted cropland. They 

will be in proposed new subsection (b). In addition, the agencies propose to delete a crossreference in the existing waste treatment system exclusion to an EPA regulation that is no longer 
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in the Code of Federal Regulations. The parenthetical to be deleted states: “(other than cooling 

ponds as defined in 40 CFR 423.11(m) which also meet the criteria of this definition).” The 

agencies do not propose any substantive changes to this exclusion. In fact, the agencies do not 

propose to make conforming changes to ensure that each of the existing definitions of the waters 

of the United States for the various CWA programs have the exact same language with respect to 

the waste treatment system exclusion. The regulations implementing the various CWA programs 

were promulgated and amended at different times and therefore there are some differences in 

language. For example, EPA’s regulations for the Section 402 program state: 

Waste treatment systems, including treatment ponds or lagoons designed to meet 

the requirements of CWA (other than cooling ponds as defined in 40 CFR 

423.11(m) which also meet the criteria of this definition) are not waters of the 

United States. This exclusion applies only to manmade bodies of water which 

neither were originally created in waters of the United States (such as disposal 

area in wetlands) nor resulted from the impoundment of waters of the United 

States. [See Note 1 of this section.] 

Note: At 45 FR 48620, July 21, 1980, the Environmental Protection Agency 

suspended until further notice in §122.2, the last sentence, beginning “This 

exclusion applies . . .” in the definition of “Waters of the United States.” This 

revision continues that suspension.i i Editorial Note: The words “This revision” 

refer to the document published at 48 FR 14153, Apr. 1, 1983.

40 C.F.R. 122.2.

The Corps’ regulations implementing Section 404 state: “Waste treatment systems, 

including treatment ponds or lagoons designed to meet the requirements of CWA (other than 
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cooling ponds as defined in 40 CFR 423.11(m) which also meet the criteria of this definition) are 

not waters of the United States.” 33 C.F.R. 328.3. The agencies do not propose to address the 

substance of the waste treatment system exclusion and thus will leave each regulation as is with 

the exception of deleting the cross-reference.

In addition, this regulation does not address or change in any way the many statutory 

exemptions from CWA requirements. Thus, the proposed rule does not affect any of the 

exemptions from CWA sections 402 and 404 permitting requirements provided by CWA section 

404(f), including those for normal agriculture, forestry and ranching practices. CWA section 

404(f); 40 C.F.R. § 232.3; 33 C.F.R. § 323.4. The proposed rule also does not address the 

statutory and regulatory exemptions from NPDES permitting requirements for agricultural 

stormwater discharges and return flows from irrigated agriculture. CWA section 402(l)(1) (“The 

Administrator shall not require a permit under this section for discharges composed entirely of 

return flows from irrigated agriculture. . . .”); CWA section 502(14)(“[The] term [point source] 

does not include agricultural stormwater discharges and return flows from irrigated 

agriculture.”); 40 C.F.R. § 122.3(f) (return flows from irrigated agriculture are excluded from the 

NPDES program); 40 C.F.R. § 122.2 (The term “point source” “does not include return flows 

from irrigated agriculture or agricultural storm water runoff.”).

Finally, in new paragraphs (b)(3) through (b)(5), the agencies propose to, for the first 

time by rule, exclude some waters and features that the agencies have by longstanding practice 

generally considered not to be waters of the United States. Specifically, the agencies propose

that the following are not waters of the United States:

(3) Artificially irrigated areas that would revert to upland should application of 

irrigation water to that area cease; artificial lakes or ponds created by excavating 
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and/or diking dry land and used exclusively for such purposes as stock watering, 

irrigation, settling basins, or rice growing; artificial reflecting pools or swimming 

pools created by excavating and/or diking dry land; small ornamental waters 

created by excavating and/or diking dry land for primarily aesthetic reasons; 

water-filled depressions created incidental to construction activity; groundwater 

drained through subsurface drainage systems; gullies and rills; non-wetland 

swales; and puddles;

(4) Ditches that are excavated wholly in uplands, drain only uplands or nonjurisdictional waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other 

waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. 

Most of these features and waters have been identified by the agencies as generally not 

waters of the United States in previous preambles or guidance documents. The agencies’ have 

always preserved the authority to determine in a particular case that one of these waters was a 

water of the United States. One of the agencies’ goals in this proposed rule is to increase clarity 

and certainty about the scope of waters of the United States. To that end, the agencies propose 

not simply that these features and waters are “generally” not waters of the United States, but that 

they are expressly not waters of the United States by rule. Under this proposal, the agencies 

would not retain the authority to determine that one of these waters was a water of the United 

States by, for example, finding that the water had a significant nexus pursuant to the other waters 

provision at (a)(7). These waters would not be jurisdictional by definition.
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A similar list of waters and features not generally waters of the United States was 

provided by the Corps in a 1986 preamble to the existing rule defining waters of the United 

States ( 51 Fed. Reg. 41206, 41217 (November 13, 1986)) and by the EPA in a 1988 preamble 

(53 FR 20764 (June 6, 1988)). In today’s proposed rule, the agencies have clarified and added 

to the list in order to provide a full description of the waters that will not be waters of the United 

States.

Today’s proposed rule states that waters of the United States do not include “artificially 

irrigated areas that would revert to upland should application of irrigation water to that area 

cease.” In the 1986 and 1988 preambles, the agencies stated that they “...generally do not 

consider the following waters to be “Waters of the United States” . . . (b) Artificially irrigated 

areas which would revert to upland if the irrigation ceased.” The Corps also addressed this issue 

in a regulatory guidance letter. RGL 07-02 at 3 n.1. 

The next few items in this proposed rule are features that Congress did not intend to 

protect under the CWA: “artificially irrigated areas that would revert to upland should 

application of irrigation water to that area cease; artificial lakes or ponds created by excavating 

and/or diking dry land and used exclusively for such purposes as stock watering, irrigation, 

settling basins, or rice growing; artificial reflecting pools or swimming pools created by 

excavating and/or diking dry land; small ornamental waters created by excavating and/or diking 

dry land for primarily aesthetic reasons; water-filled depressions created incidental to 

construction activity; groundwater drained through subsurface drainage systems; gullies and rills;

non-wetland swales; and puddles” The agencies have generally not considered these to be 

hydrologic features and therefore not “waters of the United States” in preambles or in .
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Gullies are relatively deep channels that are ordinarily formed on valley sides and floors 

where no channel previously existed. They are commonly found in areas with low-density 

vegetative cover or with soils that are highly erodible. See, e.g., N.C. Brady and R.R. Weil, The 

Nature and Properties of Soils, 13th Edition (Upper Saddle River, NJ: Prentice Hall, 2002). Rills 

are formed by overland water flows eroding the soil surface during rain storms. See, e.g., L.B. 

Leopold, A View of the River (Cambridge: Harvard University Press, 1994). Rills are less 

permanent on the landscape than streams and typically lack an OHWM, whereas gullies are 

younger than streams in geologic age; time has shaped streams into geographic features distinct 

from gullies and rills. See, e.g., American Society of Civil Engineers, Task Committee on 

Hydrology Handbook, Hydrology Handbook (ASCE Publications, 1996). The two main 

processes that result in the formation of gullies are downcutting and headcutting, which are 

forms of longitudinal (incising) erosion. These actions ordinarily result in erosional cuts that are 

often deeper than they are wide, with very steep banks, often small beds, and typically only carry 

water during precipitation events. The principal erosional processes that modify streams are also 

downcutting and headcutting. In streams, however, lateral erosion is also very important. The 

result is that streams, except on steep slopes or where soils are highly erodible, are characterized 

by the presence of bed and banks as compared to typical erosional features that are more deeply 

incised. It should be noted that some features that are named “gullies” are in fact ephemeral 

streams; such features where they are tributaries as defined by this rule would be considered 

“waters of the United States.” 

Non-wetland natural and man-made swales would not be waters of the United States 

under this proposal. In certain circumstances, however, swales include areas that meet the 

regulatory definition of “wetlands.” Swales generally are considered wetlands when they meet 
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the applicable criteria in the Corps of Engineers Wetland Delineation Manual and the appropriate 

regional supplement to that Wetland Delineation Manual. Wetland swales would be evaluated as 

adjacent waters under proposed (a)(6) or as “other waters” under proposed (a)(7) depending 

upon whether they meet the proposed definition of adjacent.

Finally, under paragraphs (b)(4) and (b)(5), the agencies are proposing to clearly exempt 

from the definition of waters of the United States two types of ditches: “ditches that are 

excavated wholly in uplands, drain only uplands or non-jurisdictional waters, and have no more 

than ephemeral flow” and “ditches that do not contribute flow, either directly or through other 

waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this section.” The 

agencies have long distinguished between ditches that are waters of the United States and ditches 

that will generally not be treated as waters of the United States. With this proposal, the agencies 

would clearly establish, by rule, that certain ditches are not waters of the United States. Other 

ditches, if they meet the new proposed definition of “tributary” would continue to be waters of 

the United States, as they have been under the agencies longstanding implementation of the 

statute and regulations.

The first type of ditches that are excluded need to meet all three criteria: (1) they are 

excavated wholly in uplands; (2) they drain only uplands or non-jurisdictional waters; and (3) 

they have no more than ephemeral flow, that is, do not intersect groundwater. Ditches that are 

excavated wholly in uplands means ditches that at no point along their length are excavated in a 

jurisdictional wetland (or other water). Members of the public should consider whether a 

wetland is jurisdictional before constructing a ditch that would drain the wetland and connect 

either directly or through other waterbodies to an (a)(1) through (a)(3) water. The ditch must 

also contain no more than ephemeral flow to be excluded under this proposed provision. 
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Ephemeral flow means that the flow in the ditch occurs only during, or for a short duration after, 

precipitation events because it does not intersect groundwater. This exclusion is generally 

consistent with agency policy for decades and as articulated in the 2008 Rapanos guidance which 

stated that the agencies generally would not assert jurisdiction over “ditches (including roadside 

ditches) excavated wholly in and draining only uplands and that do not carry a relatively 

permanent flow of water.” 

The other type of ditch that would not be a water of the United States is ditches that do 

not contribute flow, either directly or through other waterbodies, to a water identified in 

paragraphs (a)(1) through (a)(3) of this section. Essentially, ditches that do not contribute flow 

to the tributary system of a traditional navigable water, interstate water or territorial sea would 

not be waters of the United States.

It is important to note, however, that even when not jurisdictional waters, these nonwetland swales and specific types of ditches may still be a surface hydrologic connection for 

purposes of the proposed definition of adjacent under section (a)(6). For example, a wetland 

may be a “water of the United States,” meeting the proposed definition of “neighboring” because 

it is connected to a tributary by a non-jurisdictional ditch. In addition, these geographic features 

may function as “point sources” (i.e., “discernible, confined and discrete conveyance[s]” under 

CWA section 502(14)), such that discharges of pollutants to waters through these features would 

be subject to other CWA regulations (e.g., CWA section 402).

IV. Related Acts of Congress, Executive Orders, and Agency Initiatives

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: 
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Improving Regulation and Regulatory Review

Under Executive Order 12866 (58 FR 51735, October 4, 1993), this action is a 

“significant regulatory action” because it raises novel legal or policy issues. Accordingly, the 

EPA and the Corps submitted this action to the Office of Management and Budget (OMB) for 

review under Executive Orders 12866 and 13563 (76 FR 3821, January 21, 2011) and any 

changes made in response to OMB recommendations have been documented in the docket for 

this action.

In addition, the EPA and the Corps of Engineers prepared an analysis of the potential 

costs and benefits associated with this action. This analysis is contained in “Economic Analysis 

of Proposed Revised Definition of Waters of the United States.” A copy of the analysis is 

available in the docket for this action. The costs and benefits incurred of this proposed action are 

considered indirect because the action involves a definitional change to a term that is used in the 

implementation of a variety of CWA programs. Each of these programs subsequently imposes 

direct or indirect costs as a result of implementation of their specific regulations. The definition 

of “waters of the U.S. ,” by itself, imposes no direct costs. 

B. Paperwork Reduction Act 

This action does not impose any information collection burden under the provisions of 

the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. Burden is defined at 5 CFR 1320.3(b). An 

Agency may not conduct or sponsor, and a person is not required to respond to, a collection of 

information unless it displays a currently valid OMB control number. The OMB control numbers 

for EPA’s CWA section 402 program may be found at 40 CFR pt. 9.1. (OMB Control No. 2040-

0004, EPA ICR No. 0229.19). For the CWA section 404 regulatory program, the current OMB 
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approval number for information requirements is maintained by the Corps of Engineers (OMB 

approval number 0710–0003, expires August 31, 2012). However, there are no new approval or 

application processes required as a result of this rulemaking that necessitate a new ICR. 

C. Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a 

regulatory flexibility analysis of any rule subject to notice-and-comment rulemaking 

requirements under the APA or any other statute unless the agency certifies that the rule will not 

have a significant economic impact on a substantial number of small entities. Small entities 

include small businesses, small organizations, and small governmental jurisdictions.

For purposes of assessing the impacts of this final action on small entities, “small entity” 

is defined as: (1) a small business that is a small industrial entity as defined in the U.S. SBA size 

standards (see 13 CFR 121.201); (2) a small governmental jurisdiction that is a government of a 

city, county, town, school district, or special district with a population of less than 50,000; or (3) 

a small organization that is any not-for-profit enterprise that is independently owned and 

operated and is not dominant in its field. 

After considering the economic impacts of this proposed rule on small entities, I certify 

that this proposed rule will not have a significant economic impact on a substantial number of 

small entities. See, e.g., Cement Kiln Recycling Coalition v. EPA, 255 F.3d 855 (D.C. Cir. 

2001); Michigan v. EPA, 213 F.3d 663 (D.C. Cir. 2000); Am. Trucking Ass’n v. EPA, 175 F.3d 

1027 (D.C. Cir. 1999); Mid-Tex Elec. Co-op, Inc. v. FERC, 773 F.2d 327 (D.C. Cir. 1985). 

Under the RFA, the impact of concern is any significant adverse economic impact on 

small entities, because the primary purpose of the initial regulatory flexibility analysis is to 
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identify and address regulatory alternatives “which minimize any significant economic impact of 

the rule on small entities.” 5 U.S.C. 603. The scope of regulatory jurisdiction in this proposed 

rule is narrower than that under the existing regulations. See 40 CFR 122.2 (defining “waters of 

the United States”). Because fewer waters will be subject to the CWA under the proposed rule 

than are subject to regulation under the existing regulations, this action will not affect small 

entities to a greater degree than the existing regulations. As a consequence, this action if 

promulgated will not have a significant adverse economic impact on a substantial number of 

small entities, and therefore no regulatory flexibility analysis is required.

The proposed rule contemplated here is not designed to “subject” any entities of any size 

to any specific regulatory burden. Rather, it is designed to clarify the statutory scope of “the 

waters of the United States, including the territorial seas” (33 U.S.C. 1362(7)), consistent with 

Supreme Court precedent. This question of CWA jurisdiction will be informed by the tools of 

statutory construction and the geographical and hydrological factors identified in Rapanos v. 

United States, 547 U.S. 715 (2006), which are not factors readily informed by the RFA. 

Nevertheless, the scope of the term “waters of the United States” is a question that has 

continued to generate substantial interest, particularly within the small business community, 

because permits must be obtained for many discharges of pollutants into those waters. In light of 

this interest, the EPA and the Corps determined to seek early and wide input from representatives 

of small entities while formulating a proposed definition of this term that reflects the intent of 

Congress consistent with the mandate of the Supreme Court’s decisions. Such outreach, although 

voluntary, is also consistent with the President’s January 18, 2011 Memorandum on Regulatory 

Flexibility, Small Business, and Job Creation, which emphasizes the important role small 

businesses play in the American economy. This process has enabled the agencies to hear directly 
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from these representatives, at a very preliminary stage, about how they should approach this 

complex question of statutory interpretation, together with related issues that such 

representatives of small entities may identify for possible consideration in separate proceedings. 

D. Unfunded Mandates Reform Act

This proposed rule contains no Federal mandates (under the regulatory provisions of Title 

II of the Unfunded Mandates Reform Act of 1995 (UMRA), 2 USC 1531-1538 for state, local, or 

tribal governments or the private sector. This proposed rule does not directly regulate or affect 

any entity and, therefore, is not subject to the requirements of sections 202 and 205 of UMRA.

The Agencies determined that this proposed rule contains no regulatory requirements that 

might significantly or uniquely affect small governments. Moreover, the proposed definition of 

“waters of the U.S.” applies broadly to CWA programs and the subsequently affected entities, 

which are not uniquely applicable to small governments. Thus, this proposed rule is not subject 

to the requirements of section 203 of UMRA.

E. Executive Order 13132: Federalism

This action does not have federalism implications. It will not have substantial direct 

effects on the States, on the relationship between the national government and the States, or on 

the distribution of power and responsibilities among the various levels of government. This 

proposed rule seeks to clarify the definition of the extent of CWA jurisdiction established by 

statute. State and local governments have well-defined and long-standing relationships in 

implementing affected CWA programs and these relationships will not be altered. Thus, 

Executive Order 13132 does not apply to this action. In the spirit of Executive Order 13132, and 
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consistent with EPA and Corps policy to promote communications between the agencies and 

State and local governments, the agencies specifically solicit comment on this proposed action 

from State and local officials. 

F. Executive Order 13175: Consultation and Coordination With Indian Tribal 

Governments

Subject to the Executive Order (EO) 13175 (65 FR 67249, November 9, 2000) Agencies 

may not issue a regulation that has tribal implications, that imposes substantial direct compliance 

costs, and that is not required by statute, unless the Federal government provides the funds 

necessary to pay the direct compliance costs incurred by tribal governments, or the Agencies 

consult with tribal officials early in the process of developing the proposed regulation and 

develops a tribal summary impact statement. This action does not have tribal implications as 

specified in EO 13175.

In the spirit of EO 13175, and consistent with EPA and Corps policy to promote 

communications between the agencies and tribal governments, the agencies specifically solicit 

additional comment on this proposed action from tribal officials.

G. Executive Order 13045: Protection of Children From Environmental Health and 

Safety Risks

Executive Order 13045 (62 FR 19885, April 23, 1997) applies only to those 

regulatory actions concerning health or safety risks where the analysis required under 

section 5-501 of the EO has the potential to influence the regulation. This action is not 
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subject to EO 13045 because the environmental health or safety risks addressed by this 

action do not present a disproportionate risk to children.

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect 

Energy Supply, Distribution, or Use

This action is not a “significant energy action” as defined in Executive Order 

13211 (66 FR 28355 (May 22, 2001)), because it is not likely to have a significant 

adverse effect on the supply, distribution or use of energy. 

I. National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of 1995 

(“NTTAA”), Public Law No. 104-113, 12(d) (15 U.S.C. 272 note) directs federal agencies to use 

voluntary consensus standards in its regulatory activities unless to do so would be inconsistent 

with applicable law or otherwise impractical. Voluntary consensus standards are technical 

standards (e.g., materials specifications, test methods, sampling procedures, and business 

practices) that are developed or adopted by voluntary consensus standards bodies. NTTAA 

directs federal agencies to provide Congress, through OMB, explanations when the Agency 

decides not to use available and applicable voluntary consensus standards. 

This proposed rulemaking does not involve technical standards. Therefore, the agencies 

are not considering the use of any voluntary consensus standards. 

J. Executive Order 12898: Federal Actions To Address Environmental Justice in 

Minority Populations and Low-Income Populations
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Executive Order (EO) 12898 (59 FR 7629 (Feb. 16, 1994)) establishes federal executive 

policy on environmental justice. Its main provision directs federal agencies, to the greatest 

extent practicable and permitted by law, to make environmental justice part of their mission by 

identifying and addressing, as appropriate, disproportionately high and adverse human health or 

environmental effects of their programs, policies, and activities on minority populations and lowincome populations in the United States. 

The agencies have determined that this proposed rule will not have disproportionately 

high and adverse human health or environmental effects on minority or low-income populations. 

The proposed rule defines the scope of waters protected under the CWA. The increased clarity 

regarding the definition of “waters of the United States” will be of benefit to all regulators, 

stakeholders, and interested parties. However, in the spirit of Executive Order 12898, we 

specifically request comment regarding potential environmental justice issues raised by the 

proposed rule, and will fully consider those comments when preparing the final rule.

K. Environmental Documentation

The U.S. Army Corps of Engineers has prepared a draft environmental assessment in 

accordance with the National Environmental Policy Act (NEPA). The Corps has made a 

preliminary determination that the Section 404 aspects of today's proposed rule does not

constitute a major Federal action significantly affecting the quality of the human environment, 

and thus preparation of an Environmental Impact Statement (EIS) will not be required. The 

proposed rule will increase and make more efficient the protection of the aquatic environment. 

Additionally, the Corps complies with NEPA programmatically for general permits, and 
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specifically for each and every standard individual permit application before making final permit 

decisions.

The implementation of the procedures prescribed in this proposed regulation would not 

authorize anyone (e.g., any landowner or permit applicant) to perform any work involving 

regulated activities in “waters of the U.S.” without first seeking and obtaining an appropriate 

CWA authorization, which concurrently documents compliance with all applicable 

environmental laws.
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Appendix A

Scientific Evidence

Overview of Scientific Literature on Aquatic Resource Connectivity and Downstream 

Effects

In preparation for this proposal, more than a thousand peer-reviewed scientific papers and other 

data that address connectivity of aquatic resources and effects on downstream waters were 

reviewed and considered. EPA’s Office of Research and Development (ORD) has prepared a 

draft peer-reviewed synthesis of published peer-reviewed scientific literature discussing the 

nature of connectivity and effects of tributaries and wetlands on downstream waters (U.S. 

Environmental Protection Agency, Connectivity of Streams and Wetlands to Downstream 

Waters: A Review and Synthesis of the Scientific Evidence, (Washington, D.C.: U.S. 

Environmental Protection Agency, 2013), hereinafter, “Report”). This draft Report similarly has 

been considered in the development of this proposal. The Report is currently undergoing peer 

review led by EPA’s Scientific Advisory Board (SAB) and is available at 

http://yosemite.epa.gov/sab/sabproduct.nsf/fedrgstr_activites/Watershed%20Connectivity%20Re

port?OpenDocument. The Report summarizes and assesses much of the currently available 

scientific literature that is part of the administrative record for this proposal. The agencies

anticipate that additional data and information will become available during the rulemaking 

process, including that provided during the public comment process, and by additional research, 

studies, and investigations that take place before the rulemaking process is concluded. At the 

conclusion of the rulemaking process, the agencies will review the entirety of the completed 
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administrative record, including the final Report reflecting SAB review, and will make any 

adjustments to the final rule deemed to be appropriate at that time. The Report is under review 

by the Science Advisory Board, and the rule will not be finalized until that review and the final 

report are complete. Part I of this Appendix provides the conclusions of the review and 

synthesis. Part II provides additional detail of the scientific literature and the agencies’ reasoning 

in support of this proposal. 

Part I: Synthesis of Peer-Reviewed Scientific Literature

Background

The draft Report prepared by ORD reviews and synthesizes the peer-reviewed scientific 

literature on the connectivity or isolation of streams and wetlands relative to large water bodies 

such as rivers, lakes, estuaries, and oceans. The purpose of the review and synthesis is to

summarize current understanding about these connections, the factors that influence them, and 

the mechanisms by which connected waters, singly or in aggregate, affect the function or 

condition of downstream waters. The focus of the Report is on surface and shallow subsurface 

connections from small or temporary streams, non-tidal wetlands, and certain open-waters. 

Specific types of connections considered in the Report include transport of physical materials 

and chemicals such as water, wood, and sediment, nutrients, pesticides, and mercury; movement 

of organisms or their seeds or eggs; and hydrologic and biogeochemical interactions occurring in 

surface and groundwater flows, including hyporheic zones and alluvial aquifers. 

The draft Report prepared by ORD consists of six chapters. Following an executive 

summary and an introduction to the Report, chapter 3 presents a conceptual framework 

describing the hydrologic elements of a watershed, the types of chemical, physical, and 
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biological connections that link them, and watershed and climatic factors that influence 

connectivity at various temporal and spatial scales. It also provides background on the structure 

and function of streams and wetlands viewed from an integrated watershed perspective. In a 

discussion of connectivity, the watershed scale is the appropriate context for interpreting 

technical evidence about individual watershed components, reviewed in subsequent chapters. 

Chapter 4 surveys the literature on stream networks (lotic systems) in terms of chemical, 

physical, and biological connections between upstream and downstream habitats. Two case 

studies from the literature examine in greater detail longitudinal connectivity and downstream 

effects in prairie streams and arid streams of the Southwest. Chapter 5 reviews the literature on 

connectivity and effects of non-tidal wetlands and certain open-waters (lentic systems) on 

downstream waters. This chapter is further subdivided into two broad categories of landscape 

settings based on directionality of hydrologic flows: bidirectional settings, in which wetlands 

and open-waters can have two-way hydrologic exchanges with other water bodies (e.g., riparian 

and floodplain wetlands and open-waters), and unidirectional settings, in which water flows only 

from the wetland or open-water towards the downstream water (e.g., most wetlands and openwaters outside of riparian areas and floodplains). Directionality of hydrologic flow was selected 

as an organizational principle for this section because it has a dominant role in determining the 

types of connectivity and downstream effects (if any) of wetlands. However, the use of these 

landscape settings for hydrologic directionality should not be construed as suggesting 

directionality of geochemical or biological flows. Also, the terms “unidirectional” and 

“bidirectional” describe the landscape setting in which wetlands and open-waters occur, and do 

not refer to wetland type or class. Four case studies from the literature examine evidence 
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pertaining to connectivity and downstream effects of oxbow lakes, Carolina and Delmarva bays, 

prairie potholes, and vernal pools in greater detail. 

Chapter 6 presents and discusses key findings and major conclusions of the review, 

which also are included at the end of each review section and in this executive summary.

Summary of Major Conclusions

Based on the review and synthesis of more than a thousand publications from the peerreviewed scientific literature, the available evidence supports three major conclusions:

1. The scientific literature demonstrates that streams, individually and cumulatively, 

exert a strong influence on the character and functioning of downstream waters. All 

tributary streams, including perennial, intermittent, and ephemeral streams, are 

chemically, physically, and biologically connected to downstream rivers via channels 

and associated alluvial deposits where water and other materials are concentrated, 

mixed, transformed, and transported. Headwater streams (headwaters) are the most 

abundant stream-type in most river networks, and supply most of the water in rivers. 

In addition to water, streams supply sediment, wood, organic matter, nutrients, 

chemical contaminants, and many of the organisms found in rivers. Streams are 

biologically connected to downstream waters by the dispersal and migration of 

aquatic and semi-aquatic organisms, including fish, amphibians, plants, 

microorganisms, and invertebrates, that use both up- and downstream habitats during 

one or more stages of their life cycles, or provide food resources to downstream 

communities. Chemical, physical, and biological connections between streams and 

downstream waters interact via processes such as nutrient spiraling, in which stream 
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communities assimilate and chemically transform large quantities of nitrogen and 

other nutrients that would otherwise increase nutrient loading downstream. 

2. Wetlands and open-waters in landscape settings that have bidirectional hydrologic 

exchanges with streams or rivers (e.g., wetlands and open-waters in riparian areas and 

floodplains) are chemically, physically, and biologically connected with rivers via the 

export of channel-forming sediment and woody debris, temporary storage of local 

groundwater that supports baseflow in rivers, and transport of stored organic matter. 

They remove and transform excess nutrients such as nitrogen and phosphorus. They 

provide nursery habitat for breeding fish, colonization opportunities for stream 

invertebrates, and maturation habitat for stream insects. Moreover, wetlands in this 

landscape setting serve an important role in the integrity of downstream waters 

because they also act as sinks by retaining floodwaters, sediment, nutrients, and 

contaminants that could otherwise negatively impact the condition or function of 

downstream waters. 

3. Wetlands in landscape settings that lack bidirectional hydrologic exchanges with 

downstream waters (e.g., many prairie potholes, vernal pools, and playa lakes) 

provide numerous functions that can benefit downstream water quality and integrity.

These functions include storage of floodwater; retention and transformation of 

nutrients, metals, and pesticides; and re-charge of groundwater sources of river 

baseflow. The functions and effects of this diverse group of wetlands, which the 

Report refers to as “unidirectional wetlands,” affect the condition of downstream 

waters if there is a surface or shallow subsurface water connection to the river 

network. In unidirectional wetlands that are not connected to the river network 
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through surface or shallow subsurface water, the type and degree of connectivity 

varies geographically within a watershed and over time. Because such wetlands occur 

on a gradient of connectivity, it is difficult to generalize about their effects on

downstream waters. Generalization for this class is further complicated because, for 

certain functions (e.g., sediment removal and water storage), downstream effects are 

due to wetland isolation, rather than connectivity. The literature reviewed does not 

provide sufficient information to evaluate or generalize about the degree of 

connectivity (absolute or relative) or the downstream effects of wetlands in 

unidirectional landscape settings. However, evaluations of individual geographically 

isolated wetlands or groups of geographically isolated wetlands could be possible 

through case-by-case analysis. Further, while the review did not specifically address 

other unidirectional water bodies, the conclusions apply to these water bodies (e.g., 

ponds and lakes that lack surface water inlets) as well, since the same principles

govern hydrologic connectivity between these water bodies and downstream waters.

Section 3 below provides an overview of the conceptual framework, with further 

discussion of the key findings for streams, riparian and floodplain areas, and unidirectional 

wetlands. 

1. Conceptual Framework Overview

Connectivity is a foundational concept in hydrology and freshwater ecology. The 

structure and function of downstream waters are highly dependent on the constituent materials 

contributed by and transported through water bodies located elsewhere in the watershed. Most 

of the materials in a river, including water, sediment, wood, organic matter, nutrients, chemical 

contaminants, and certain organisms, originate outside of the river, from upstream tributaries, 
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wetlands, or other components of the river system, and are transported to the river by water 

movement, wind, or other means. Therefore, streams and wetlands fundamentally affect river 

structure and function by altering transport of various types of materials to the river. This 

alteration of material transport depends on two key factors: (1) connectivity (or isolation) 

between streams, wetlands and rivers that enables (or prevents) the movement of materials 

between the system components; and (2) functions within streams and wetlands that supply, 

remove, transform, provide refuge for, or delay transport of materials. 

The ORD Report defines connectivity as the degree to which components of a system are 

joined, or connected, by various transport mechanisms. Connectivity is determined by the 

characteristics of both the physical landscape and the biota of the specific system. Isolation is 

the opposite of connectivity; or the degree to which system components are not joined. Both 

connectivity and isolation have important effects on downstream waters. For example, stream 

channels convey water and channel-forming sediment to rivers, whereas wetlands that lack 

output channels can reduce flooding and store excess sediment. Materials transport connects 

different ecosystem types, at multiple spatial and temporal scales. For example, streams flowing 

into and out of wetlands or between lakes form continuous or seasonal connections across 

ecosystem boundaries. Similarly, aquatic food webs connect terrestrial ecosystems, streams, 

wetlands, and downstream waters. 

Water movement through the river system is the primary, but certainly not the only, 

mechanism providing physical connectivity within river networks. It provides a “hydraulic 

highway” that transports chemical, physical, and biological materials associated with the water 

(e.g., sediment, woody debris, contaminants, organisms). Because the movement of water is 

fundamental to understanding watershed connectivity, Chapter 3 begins with a review and an 
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explanation of the hydrologic foundation of river systems, and terms and concepts used 

throughout the Report are defined. 

Numerous factors influence watershed connectivity. Climate, watershed topography, soil 

and aquifer permeability, the number and types of contributing waters, their spatial distribution 

in the watershed, interactions among aquatic organisms, and human alteration of watershed 

features, among other things, can act individually or in concert to influence stream and wetland 

connectivity to, and effects on, downstream waters. For example, all else being equal, materials 

traveling shorter distances could enter the river with less transformation or dilution, thus 

increasing a beneficial or harmful effect. In other cases, sequential transformations such as 

nutrient spiraling (defined and discussed below) connect distant water bodies and produce 

beneficial effects on downstream waters. Infrequent events that temporarily connect nearby or 

distant streams or wetlands to rivers also can have large, long-lasting effects. Most of the major 

changes in sediment load and river channel structure that are critical to maintaining river 

health—including meanders of rivers in floodplains and creation of oxbow lakes—are a result of 

large floods that provide infrequent, intense connections with more distant streams and riparian 

or floodplain waters. 

Based on a review of the peer-reviewed scientific literature, the Report identifies five

functions by which streams, wetlands, and open-waters influence material transport into 

downstream waters: 

• Source: the net export of materials, such as water and food resources

• Sink: the net removal or storage of materials, such as sediment and contaminants

• Refuge: the protection of materials, especially organisms
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• Transformation: the transformation of materials, especially nutrients and chemical 

contaminants, into different physical or chemical forms

• Lags: the delayed or regulated release of materials, such as storm water

These functions are not static or mutually exclusive (e.g., a wetland can be both a source 

of organic matter and a sink for nitrogen) and can change over time (e.g., one wetland can be a 

water sink when evapotranspiration is high and a water source when evapotranspiration is low). 

Further, some functions work in conjunction with others. For example, a lag function can 

include transformation of materials prior to their delayed release. In a particular stream, wetland, 

or open-water, the presence or absence of these functions depends upon the biota, hydrology, and 

environmental conditions in the watershed. 

When considering effects on downstream waters, it is helpful to distinguish between 

actual function and potential function of a stream, wetland, or open-water. For example, a 

wetland with appropriate conditions for denitrification is a potential sink for nitrogen, a nutrient 

that can be a contaminant when present in high concentrations. This function is conditional; if 

nitrogen were to enter a wetland (from agricultural runoff, for example), the wetland has the 

capacity to remove this nitrogen from the water. The wetland will not serve this function, 

however, if no nitrogen enters the wetland. Even if a stream or wetland is not currently serving 

an actual function, it has the potential to provide that function when a new material enters it, or 

when environmental conditions change. Thus, potential functions play a critical role in 

protecting those waters from future impacts. 

2. Discussion of Major Conclusions
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A. Streams 

The scientific literature clearly demonstrates that streams, individually or cumulatively, 

exert a strong influence on the character and functioning of downstream waters. All tributary 

streams, including perennial, intermittent, and ephemeral streams, are chemically, physically, 

and biologically connected to downstream rivers via channels and associated alluvial deposits 

where water and other materials are concentrated, mixed, transformed, and transported. 

Headwater streams (headwaters) are the most abundant stream-type in most river networks, and 

supply most of the water in rivers. In addition to water, streams supply sediment, wood, organic 

matter, nutrients, chemical contaminants, and many of the organisms found in rivers. Streams 

are biologically connected to downstream waters by dispersal and migration of aquatic and semiaquatic organisms, including fish, amphibians, plants, microorganisms, and invertebrates, that 

use both up- and downstream habitats during one or more stages of their life cycles, or provide 

food resources to downstream communities. Physical, chemical, and biological connections 

between streams and downstream waters interact via processes such as nutrient spiraling, in 

which stream communities assimilate and chemically transform large quantities of nitrogen and 

other nutrients that would otherwise increase nutrient loading downstream. 

Key findings:

a. Streams are hydrologically connected to downstream waters via channels that convey 

surface and subsurface water year-round (perennial flow), weekly to seasonally 

(intermittent flow), or only in direct response to precipitation (ephemeral flow). 

Streams are the dominant source of water in most rivers, and the great majority of 

tributaries are perennial, intermittent, and ephemeral headwater streams. For 

example, headwater streams, which are the smallest channels where stream flows 
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begin, are the source of approximately 60% of the total mean annual flow to all 

northeastern U.S. streams and rivers. 

b. Headwaters convey water into local storage compartments such as ponds, shallow 

aquifers, or river banks and into regional and alluvial aquifers. These local storage 

compartments are important sources of water for baseflow in rivers. The ability of 

streams to keep flowing even during dry periods typically depends on the delayed 

(lagged) release of local groundwater, also referred to as shallow groundwater,

originating from these water sources, especially in areas with shallow groundwater 

tables and pervious subsurfaces. For example, in the southwestern United States, 

short-term shallow groundwater storage in alluvial floodplain aquifers, with gradual 

release into stream channels by intermittent and ephemeral streams, is a major source 

of annual flow in rivers. 

c. Even infrequent flows through ephemeral or intermittent channels influence 

fundamental biogeochemical processes by connecting the channel and shallow 

groundwater with other landscape elements. Infrequent, high-magnitude events are 

especially important for transmitting materials from headwater streams in most river 

networks. For example, headwater streams, including ephemeral and intermittent 

streams, shape river channels by accumulating and gradually or episodically releasing 

stored materials such as sediment and large woody debris. These materials provide 

substrate, habitat for aquatic organisms, and slow the flow of water through channels.

d. Connectivity between streams and rivers provides opportunities for materials, 

including nutrients and chemical contaminants, to be sequentially altered as they are 

transported downstream. Although highly efficient at transport of water and other 
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physical materials, streams are not pipes. They are dynamic ecosystems with 

permeable beds and banks that interact with terrestrial and aquatic ecosystems above 

and below the surface. The connections formed by surface and subsurface 

streamflows act as a series of complex chemical, physical, and biological alterations 

that occur as materials move through different parts of the river system. The amount 

and quality of such materials that eventually reach a river are determined by the 

aggregate effect of these sequential alterations that begin at the source waters, which 

can be at some distance from the river. The greater the distance a material travels 

between a particular stream reach and the river, the greater the opportunity for that 

material to be altered in intervening stream reaches, which can allow for uptake, 

assimilation, or beneficial transformation. One example of sequential alteration with 

significant beneficial effects on downstream waters is the process of nutrient 

spiraling, in which nutrients entering headwater streams are transformed by various 

aquatic organisms and chemical reactions as they are transported downstream by 

streamflow. Nutrients which enter the headwater stream (e.g., via overland flow) are 

first removed from the water column by streambed algal and microbial populations. 

Fish or insects feeding on algae and microbes take up some of those nutrients, which 

are subsequently released back to the stream via excretion and decomposition, and the 

cycle is repeated. In each phase of the cycling process—from dissolved inorganic 

nutrients in the water column, through microbial uptake, subsequent transformations 

through the food web, and back to dissolved nutrients in the water column—nutrients 

are subject to downstream transport. Stream and wetland capacities for nutrient 
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cycling have important implications for the form and concentration of nutrients 

exported to downstream waters. 

e. The literature review found strong evidence that headwater streams function as 

nitrogen sources (export) and sinks (uptake and transformation) for river networks. 

One study estimated that rapid nutrient cycling in small streams that were free from 

agricultural or urban impacts removed 20–40% of the nitrogen that otherwise would 

be delivered to downstream waters. Nutrients are necessary to support aquatic life, 

but excess nutrients create conditions leading to eutrophication and hypoxia, in which 

oxygen concentrations fall below the level necessary to sustain most within and nearbed animal life. Thus, the role of streams in influencing nutrient loads can have 

significant repercussions for hypoxic areas in downstream waters. 

f. Headwaters provide critical habitat during one or more life cycle stages of many 

organisms capable of moving throughout river networks. This review found strong 

evidence that headwaters provide habitat for complex life-cycle completion, refuge 

from predators or adverse physical conditions in rivers, and reservoirs of genetic- and 

species-level diversity. Use of headwater streams as habitat is especially obvious for 

the many species that migrate between small streams and marine environments during 

their life cycles (e.g., Pacific and Atlantic salmon, American eels, certain lamprey 

species), and the presence of these species within river networks provides robust 

evidence of biological connections between headwaters and larger rivers. In prairie 

streams, many fishes swim upstream into tributaries to release eggs, which develop as 

they are transported downstream. Small streams also provide refuge habitat for 

riverine organisms seeking protection from temperature extremes, flow extremes, low 
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dissolved oxygen, high sediment levels, or the presence of predators, parasites, and 

competitors. 

B. Riparian/Floodplain Waters 

Wetlands and open-waters in landscape settings that have bidirectional hydrologic 

exchanges with streams or rivers (e.g., wetlands and open-waters in riparian areas and 

floodplains) are chemically, physically, and biologically connected with rivers via the export of 

channel-forming sediment and woody debris, temporary storage of local groundwater that 

supports baseflow in rivers, and transport of stored organic matter. They remove and transform 

excess nutrients such as nitrogen and phosphorus. They provide nursery habitat for breeding fish, 

colonization opportunities for stream invertebrates, and maturation habitat for stream insects. 

Moreover, wetlands in this landscape setting serve an important role in the integrity of 

downstream waters because they also act as sinks by retaining floodwaters, sediment, nutrients, 

and contaminants that could otherwise negatively impact the condition or function of 

downstream waters. 

Key Findings:

a. Riparian areas act as buffers that are among the most effective tools for mitigating 

nonpoint source pollution. The wetland literature shows that collectively, riparian 

wetlands improve water quality through assimilation, transformation, or sequestration 

of nutrients, sediment and other pollutants—such as pesticides and metals—that can 

affect downstream water quality. These pollutants enter wetlands via various 

pathways that include various sources such as dry and wet atmospheric deposition, 

some runoff from upland agricultural and urban areas, spray drift, and subsurface 

water flows, as well as point sources such as outfalls, pipes, and ditches.
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b. Riparian and floodplain areas connect upland and aquatic environments through both 

surface and subsurface hydrologic flow paths. These areas are therefore uniquely 

situated in watersheds to receive and process waters that pass over densely vegetated 

areas and through subsurface zones before reaching streams and rivers. When 

contaminants reach a riparian or floodplain area, such materials can be sequestered in 

sediments, assimilated into the wetland plants and animals, transformed into less 

harmful forms or compounds, or lost to the atmosphere. Wetland potential for 

biogeochemical transformations (e.g., denitrification) that can improve the quality of 

water entering streams and rivers is influenced by factors present in riparian areas and 

floodplains, including anoxic conditions, shallow water tables, slow organic matter 

decomposition, wetland plant communities, permeable soils, and complex 

topography.

c. Riparian and floodplain areas can reduce flood peaks by storing and desynchronizing 

floodwaters. They also can contribute to maintenance of flow by recharging alluvial 

aquifers. Many studies have documented the ability of riparian and floodplain areas to 

reduce flood pulses by storing excess water from streams and rivers. One review of 

wetland studies reported that riparian wetlands reduced or delayed floods in 23 of 28 

studies. For example, peak discharges between upstream and downstream gauging 

stations on the Cache River in Arkansas were reduced 10–20% primarily due to 

floodplain water storage. 

d. Riparian and floodplain areas store large amounts of sediment and organic matter 

from upland areas before those sediments enter the stream. For example, riparian 
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areas have been shown to filter 80–90% of sediments leaving agricultural fields in 

North Carolina.

e. Ecosystem function within a river system is driven by interactions between the 

physical environment and the diverse biological communities living within the river 

system. Movements of organisms connect aquatic habitats and populations in 

different locations through several processes important for the survival of individuals, 

populations, and species, and for the functioning of the river ecosystem. For 

example, lateral expansion and contraction of the river in its floodplain results in an 

exchange of matter and organisms, including fish populations that are adapted to use 

floodplain habitat for feeding and spawning during high water. Refuge populations 

of aquatic plants in floodplains can become important seed sources for the river 

network, especially if catastrophic flooding scours vegetation and seed banks in other 

parts of the channel. Many invertebrates exploit temporary hydrologic connections 

between rivers and floodplain wetland habitats, moving into these wetlands to feed, 

reproduce, or avoid harsh environmental conditions and then returning to the river 

network. Amphibians and aquatic reptiles in many parts of the country commonly 

use both streams and wetlands, including wetlands in riparian and floodplain areas, to 

hunt, forage, overwinter, rest, or hide from predators.

C. Unidirectional Wetlands 

Wetlands in landscape settings that lack bidirectional hydrologic exchanges with 

downstream waters (e.g., many prairie potholes, vernal pools, and playa lakes) provide numerous 

functions that can benefit downstream water quality and integrity. These functions include 

storage of floodwater; retention and transformation of nutrients, metals, and pesticides; and re-
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charge of groundwater sources of river baseflow. The functions and effects of this diverse group 

of wetlands, hereafter referred to as “unidirectional wetlands,” clearly affect the condition of 

downstream waters if there is a surface or shallow subsurface water connection to the river 

network. In unidirectional wetlands that are not connected to the river network through surface 

or shallow subsurface water, the type and degree of connectivity varies geographically within a 

watershed and over time. Because such wetlands occur on a gradient of connectivity, it is 

difficult to generalize about their effects on downstream waters. This evaluation is further 

complicated because, for certain functions (e.g., sediment removal and water storage), 

downstream effects arise from wetland isolation, rather than connectivity. The literature 

reviewed does not provide sufficient information to evaluate or generalize about the degree of 

connectivity (absolute or relative) or the downstream effects of wetlands in unidirectional 

landscape settings. However, evaluations of connectivity of individual wetlands or groups of 

wetlands could be possible through case-by-case analysis. Further, while the review did not 

specifically address other unidirectional water bodies, the conclusions apply to these water 

bodies (e.g., ponds and lakes that lack surface water inlets) as well, since the same principals 

govern hydrologic connectivity between these water bodies and downstream waters.

Key Findings:

a. Water storage by wetlands well outside of riparian or floodplain areas can affect 

streamflow. Hydrologic models of prairie potholes in the Starkweather Coulee 

subbasin (North Dakota) that drain to Devils Lake indicate that increasing the volume 

of pothole storage across the sub-basin by approximately 60% caused simulated total 

annual streamflow to decrease 50% during a series of dry years and 20% during wet 

years. Similar simulation studies of watersheds that feed the Red River of the North 
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in North Dakota and Minnesota demonstrated qualitatively comparable results, 

suggesting that the ability of potholes to modulate streamflow may be widespread 

across portions of the prairie pothole region. This work also indicates that reducing 

wetland water storage capacity by connecting formerly isolated potholes through 

ditching or drainage to the Devils Lake and Red River basins could increase

stormflow and contribute to downstream flooding. In many agricultural areas already 

crisscrossed by extensive drainage systems, total streamflow and baseflow are 

enhanced by directly connecting potholes to stream networks. The impacts of 

changing streamflow are numerous, including altered flow regime, stream 

geomorphology, habitat, and ecology. The presence or absence of an effect of prairie 

pothole water storage on streamflow depends on many factors, including patterns of 

precipitation, topography and degree of human alteration. For examples, in parts of 

the prairie pothole region with low precipitation, low stream density, and little human 

alteration, hydrologic connectivity between prairie potholes and streams or rivers is 

likely to be low. 

b. Unidirectional wetlands act as sinks and transformers for various pollutants, 

especially nutrients, which pose a serious pollution problem in the United States. In 

one study, sewage wastewaters were applied to forested unidirectional wetlands in 

Florida for a period of 4.5 years. More than 95% of the phosphorus, nitrate, 

ammonium, and total nitrogen were removed by the wetland during the study period, 

and 66-86% of the nitrate removed was attributed to the process of denitrification. In 

another study, sizeable phosphorus retention occurred in unidirectional marshes that 

comprised only 7% of the lower Lake Okeechobee basin area in Florida. A 
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unidirectional bog in Massachusetts was reported to sequester nearly 80% of nitrogen 

inputs from various sources, including atmospheric deposition, and prairie pothole 

wetlands in the upper Midwest were found to remove >80% of the nitrate load via 

denitrification. A large unidirectional prairie marsh was found to remove 86% of 

nitrate, 78% of ammonium, and 20% of phosphate through assimilation and 

sedimentation, sorption, and other mechanisms. Together, these and other studies 

indicate that on-site removal of nutrients by unidirectional wetlands is significant and 

geographically widespread. The effects of this removal on rivers are generally not 

reported in the literature.

c. Biological connectivity can occur between unidirectional wetlands and downstream 

waters through movement of amphibians, aquatic seeds, macroinvertebrates, reptiles, 

and mammals. Many species in those groups that use both stream and wetland 

habitats are capable of dispersal distances equal to or greater than distances between 

many unidirectional wetlands and river networks. Unidirectional wetlands can be 

hydrologically connected directly to river networks through channels, nonchannelized surface flow, or subsurface flows. A wetland surrounded by uplands is 

defined as “geographically isolated.” Our review found that in some cases, wetland 

types such as vernal pools and coastal depressional wetlands are collectively, and 

incorrectly, referred to as geographically isolated. Technically, the term 

“geographically isolated” should be applied only to the particular wetlands within a 

type or class that are completely surrounded by uplands. Furthermore, “geographic 

isolation” should not be confused with functional isolation, because geographically 
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isolated wetlands can still have hydrological and biological connections to 

downstream waters. 

d. Unidirectional wetlands occur along a gradient of hydrologic connectivity-isolation 

with respect to river networks, lakes, or marine/estuarine water bodies. This gradient 

includes, for example, wetlands that serve as origins for stream channels that have 

permanent surface water connections to the river network; wetlands with outlets to 

stream channels that discharge to deep groundwater aquifers; geographically isolated 

wetlands that have local groundwater or occasional surface water connections to 

downstream waters; and isolated wetlands that have minimal hydrologic connection 

to other water bodies (but which could include surface and subsurface connections to 

other wetlands). The existence of this gradient among wetlands of the same type or in 

the same geographic region can make it difficult to determine or generalize, from the 

literature alone, the degree to which particular wetlands (individually or as classes), 

including geographically isolated wetlands, are hydrologically connected. 

e. A related issue is that spatial scale must be considered when determining geographic 

isolation. Individual wetlands that are geographically isolated could be connected to 

downstream waters when considered as a complex (a group of interacting wetlands). 

This principle was demonstrated in a recent study that examined a depressional 

wetland complex on the Texas coastal plain. These wetlands have been considered as 

a type of geographically isolated wetlands. Collectively, however, they are 

geographically and hydrologically connected to downstream waters in the area. 

During an almost 4-year study period, nearly 20% of the precipitation that fell on the 

wetland complex flowed as surface runoff through an intermittent stream to a nearby 
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waterway, the Armand Bayou. Thus, wetland complexes could have connections to 

downstream waters through stream channels even when the individual wetland 

components are geographically isolated.

3. Closing comments

The strong hydrologic connectivity of river networks is apparent in the existence of 

stream channels that form the physical structure of the network itself. Given the discussion 

above, it is clear that streams and rivers are much more than a system of physical channels for 

conveying water and other materials downstream, but the presence of physical channels is one 

strong line of evidence for surface water connections from tributaries, or water bodies of other 

types, to downstream waters. Physical channels are defined by continuous bed-and-bank

structures, which may include apparent disruptions (such as by bedrock outcrops, braided 

channels, flow-through wetlands) associated with changes in the material and gradient over and 

through which water flows. The continuation of bed and banks down gradient from such 

disruptions is evidence of the surface connection with the channel that is up gradient of the 

perceived disruption. 

The structure and function of rivers are highly dependent on the constituent materials that 

are stored in and transported through them. Most of these materials, broadly defined here as any 

physical, chemical, or biological entity, including, but not limited to, water, heat energy, 

sediment, wood, organic matter, nutrients, chemical contaminants, and organisms, originate 

outside of the river: they originate from either the upstream river network or other components 

of the river system, and then are transported to the river by water movement or other 

mechanisms. Thus, the fundamental way in which streams and wetlands affect river structure 

and function is by altering fluxes of materials to the river. The control of material fluxes 
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depends on two key factors: (1) functions within streams and wetlands that affect material 

fluxes, and (2) connectivity (or isolation) between streams and wetlands and rivers that allows 

(or prevents) transport of materials between the systems. 

Absence of channels does not, however, mean that a wetland or open-water is isolated or 

only infrequently connected to downstream waters. Areas that are infrequently flooded by 

surface water can be connected more regularly through shallow groundwater or through dispersal 

among biological populations and communities. Such wetlands and open-waters also can reduce 

flood peaks by storing flood waters, filter large amounts of sediment and nutrients from upland 

areas, influence stream geomorphology by providing woody debris and sediment, and regulate 

stream temperature. They also serve as sources of food for river biota and sources of genetic 

diversity for populations of stream invertebrates. 

Unidirectional wetlands can reduce and attenuate floods through water storage, and can 

recharge groundwater, thereby contributing to stream and river baseflow. These wetlands also 

affect nutrient delivery and improve water quality by functioning as sources of food and as sinks 

for metals, pesticides, excess nutrients. Biological connectivity can also occur between 

unidirectional wetlands and downstream waters, through movement of amphibians, aquatic 

insects, aquatic reptiles, migratory birds, and riverine mammals that require or opportunistically 

use both river and wetland or open-water habitats. However, given a geographically isolated 

wetland for which a surface water connection cannot be observed, it is difficult to assess its 

degree of connectivity with the river network without site-specific data.

Additionally, caution should be used in interpreting connectivity for wetlands based on 

their being designated as “geographically isolated” since (a) the term can be mistakenly applied 

to a heterogeneous group of wetlands that can include wetlands that are not geographically 
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isolated, (b) wetlands with permanent channels could be miscategorized as geographically 

isolated if the designation is based on maps or imagery with inadequate spatial resolution, 

obscured views, etc., and (c) wetland complexes could have connections to downstream waters 

through stream channels even if individual wetlands within the complex are geographically 

isolated. Thus, the term “geographically isolated” should only be applied to groups of wetlands if 

they fit the technical definition (i.e., they are surrounded by uplands). Further, even 

geographically isolated wetlands can be connected to other wetlands and downstream waters 

through groundwater connections, occasional spillage, or biological connections. Thus, the term 

“geographically isolated” should not be used to infer lack of hydrologic, chemical, or biological 

connectivity.

Lastly, to understand the health, behavior, and sustainability of downstream waters, 

effects of small water bodies in a watershed need to be considered in aggregate. The 

contribution of material by a particular stream and wetland might be small, but the aggregate 

contribution by an entire class of streams and wetlands (e.g., all ephemeral streams in the river 

network) might be substantial. For example, western vernal pools typically occur within “vernal 

pool landscapes” or complexes of pools in which swales connect pools to each other and to 

seasonal streams, and in which the hydrology and ecology are tightly coupled with the local and 

regional geological processes that formed them. The vernal pool basins, swales, and seasonal 

streams are part of a single surface water and shallow groundwater system connected to the river 

network when seasonal precipitation exceeds storage capacity of the wetlands. Since rivers 

develop and respond over time and are functions of the whole watershed, understanding the 

integration of contributions and effects over time is also necessary to have an accurate 

understanding of the system, taking into account the duration and frequency of material export 
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and delivery to downstream waters. In addition, when considering the effect of an individual 

stream or wetland, it is important to include the cumulative effect of all materials that originate 

from it, rather than each material individually, to understand that water body’s influence on 

downstream waters. 

Part II: Additional Scientific Support 

i. Tributaries

The agencies propose that all waters that meet the proposed definition of tributary are 

waters of the United States because they meet Justice Kennedy’s test for jurisdiction under 

Rapanos. In other words, the agencies are asserting that all tributaries have a significant nexus 

with traditional navigable waters, interstate waters, and/or the territorial seas. EPA’s and the 

Corps’ longstanding definition of waters of the United States has included tributaries. That 

regulation was based on the agencies’ historic view of the scope of the CWA and the general 

scientific understanding about the ecological and hydrological relationship between waters. 

Tributaries have a substantial impact on the chemical, physical, and biological integrity 

of waters into which they eventually flow—including traditional navigable waters, interstate 

waters, and the territorial seas. The great majority of tributaries are headwater streams, and 

whether they are perennial, intermittent, or ephemeral, they play an important role in the 

transport of water, sediments, organic matter, nutrients, and organisms to downstream 

environments. Tributaries serve to store water (thereby reducing flooding), provide 

biogeochemical functions that help maintain water quality, trap and transport sediments, 

transport, store and modify pollutants, provide habitat for plants and animals, and sustain the 
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biological productivity of downstream rivers, lakes and estuaries. These conclusions are strongly 

supported in the scientific literature, as discussed below.

Headwater streams are the smallest channels where stream flows begin, and often occur 

at the outer rims of a watershed. Typically these are first-order streams (i.e., they do not have any 

other streams flowing into them). However, headwater streams can include streams with multiple 

tributaries flowing into them and can be perennial, intermittent or ephemeral, but are still located 

near the channel origins of the tributary system in a watershed.

Protection of tributaries under the CWA is critically important because they serve many 

important functions which directly influence the integrity of downstream waters. It is necessary 

to regulate the entire tributary system to fulfill the objective of the CWA, because discharges of 

pollutants into the tributary system adversely affects the physical, chemical, and biological 

integrity of these waters. For example, destruction or modification of headwater streams has 

been shown to affect the integrity of downstream waters, in part through changes in hydrology, 

chemistry and stream biota. M.C. Freeman, et al., “Hydrologic Connectivity and the 

Contribution of Stream Headwaters to Ecological Integrity at Regional Scales,” Journal of the 

American Water Resources Association 43:5-14. (2007); M.S. Wipfli., et al., “Ecological 

Linkages between Headwaters and Downstream Ecosystems: Transport of Organic Matter, 

Invertebrates, and Wood Down Headwater Channels,” Journal of the American Water Resources 

Association 43:72-85 (2007). Additionally, activities such as discharging a pollutant into one part 

of the tributary system are well-documented to affect, at times, other parts of the system, even 

when the point of discharge is far upstream from the navigable water that experiences the effect 

of the discharge. In order to protect traditional navigable waters, interstate waters, and the 
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territorial seas it is also critically important to protect tributaries as defined in today’s proposal 

that are upstream from those waters.

A. The Agencies Have Concluded that Tributaries, as Defined in the Proposed Rule, 

Have a Significant Nexus

The scientific literature documents that tributary streams, including perennial, 

intermittent, and ephemeral streams, and certain categories of ditches are integral parts of river 

networks because they are directly connected to rivers via permanent surface features (channels 

and associated alluvial deposits) that concentrate, mix, transform, and transport water and other 

materials, including food resources, downstream. Tributaries transport, and often transform, 

chemical elements and compounds, such as nutrients, ions, dissolved and particulate organic 

matter and contaminants, influencing water quality, sediment deposition, nutrient availability, 

and biotic functions in rivers. Streams also are biologically connected to downstream waters by 

dispersal and migration, processes which have critical implications for aquatic populations of 

organisms that use both headwater and river or open water habitats to complete their life cycles 

or maintain viable populations. The scientific literature clearly demonstrates that cumulatively, 

streams exert strong influence on the character and functioning of rivers. In light of these well 

documented connections and functions, the agencies concluded that tributaries, as defined, alone 

or in combination with other tributaries in a watershed, significantly affect the chemical, physical 

and biological integrity of a traditional navigable water, interstate water, or the territorial seas. 

The scientific literature supports this conclusion for ephemeral tributaries, as well as for 

intermittent and perennial tributaries; for tributaries both near to and far from the downstream 

traditional navigable water, interstate water, or the territorial seas; and for natural tributaries or 

man-altered tributaries, such as ditches and canals.
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The discussion below summarizes the key points in the literature regarding the chemical,

physical, and biological connections and functions of tributaries that significantly affect 

downstream waters. In addition, the evidence regarding headwater streams and non-perennial 

streams, types of tributaries whose important functional relationships to downstream traditional 

navigable waters and interstate waters might not be obvious, is summarized. The scientific 

literature does not use legal terms like “traditional navigable water,” “interstate water,” or “the 

territorial seas.” Rather, the literature assesses tributaries in terms of their connections to and 

effects on downstream waters in a watershed. While the agencies define as “waters of the United 

States” tributaries only in watersheds which drain to a traditional navigable water, interstate 

water, or the territorial seas, that distinction does not affect the conclusions of the scientific 

literature with respect to the effects of tributaries on downstream waters.

B. Tributaries Significantly Affect the Physical Integrity of (a)(1) through (a)(3) 

Waters

Tributaries, even when seasonally dry, are the dominant source of water in most rivers, 

rather than direct precipitation or groundwater input to main stem river segments. See, e.g., 

Report at 4-3 (citing T.C. Winter, 2007, “The role of groundwater in generating streamflow in 

headwater areas and in maintaining base flow,” Journal of the American Water Resources 

Association 43:15-25; P.A. Bukaveckas, “Rivers,” in G.E. Likens, ed., Encyclopedia of Inland 

Waters, Vol. 1 (Elsevier: Oxford, 2009)). Distant headwaters with stronger connections to 

groundwater or consistently higher precipitation levels than downstream reaches contribute more 

water to downstream rivers. In the northeastern United States headwater streams contribute 

greater than 60% of the water volume in larger tributaries, including navigable rivers. See, e.g.,

id. (citing R.B. Alexander, et. al., “The role of headwater streams in downstream water quality,” 
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Journal of the American Water Resources Association 43:41-59 (2007)). The contributions of 

tributaries to river flows are often readily measured or observed, especially immediately below 

confluences, where tributary flows increase the flow volume and alter physical conditions, such 

as water temperature, in the main stream. The physical effects of tributaries are particularly clear 

after intense rainfall occurs over only the upper tributary reaches of a river network. For 

example, a study of ephemeral tributaries to the Rio Grande in New Mexico found that after a 

storm event contributions of the stormflow from ephemeral tributaries accounted for 76% of the 

flow of the Rio Grande. See, e.g., id. at 4-5 (citing E.R. Vivoni, et. al., “Analysis of a Monsoon 

Flood Event in an Ephemeral Tributary and Its Downstream Hydrologic Effects,” Water 

Resources Research 42:W03404 (2006)). A key effect of tributaries on the hydrologic response 

of river networks to storm events is dispersion, or the spreading of water output from a drainage 

basin over time. Hydrologic dispersion of connected tributaries influence the timing and volume 

of water reaching a river network outlet. See, e.g., id. at 4-5 to 4-6 (citing P. M. Saco and P. 

Kumar, “Kinematic dispersion in stream networks coupling hydraulics and network geometry,” 

Water Resources Research 38:1244 (2002)). Tributaries also can reduce the amount of water that 

reaches downstream rivers and minimize downstream flooding, often through infiltration or 

seepage through channel beds and banks or through evapotranspiration. See, e.g., id. at 4-8

(citing S.K. Hamilton, et al., “Persistence of Aquatic Refugia between Flow Pulses in a Dryland 

River System (Cooper Creek, Australia),” Limnology and Oceanography 50:743-754 (2005); J.F. 

Costelloe, et.al., “Determining Loss Characteristics of Arid Zone River Waterbodies,” River 

Research and Applications 23:715-731 (2007)). 

C. Tributaries Significantly Affect the Physical Integrity of (a)(1) through (a)(3) 

Waters
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One of the primary functions of tributaries is transporting sediment to downstream 

waters. Tributaries, particularly headwaters, shape and maintain river channels by accumulating 

and gradually or episodically releasing sediment and large woody debris into river channels. 

Sediment transport is also clearly provided by ephemeral streams. Effects of the releases of 

sediment and large woody debris are especially evident at tributary-river confluences, where 

discontinuities in flow regime and temperature clearly demonstrate physical alteration of river 

structure and function by headwater streams. Report at 4-10, 4-14. Sediment movement is critical 

for maintaining the river network, including rivers that are considered to be traditional navigable 

waters, as fluvial (produced by the action of a river or stream) sediments are eroded from some 

channel segments, and deposited in others downstream to form channel features, stream and 

riparian habitat which supports the biological communities resident downstream, and influence 

the river hydrodynamics. See, e.g., J.L. Florsheim, et al., “Bank Erosion as a Desirable Attribute 

of Rivers,” Bioscience 58: 519-29 (2008); Report at 4-9 (citing M. Church, “Bed material 

transport and the morphology of alluvial river channels,” Annual Review of Earth and Planetary 

Sciences: 325-354 (2006)). While essential to river systems, too much sediment can impair 

ecological integrity by filling interstitial spaces, blocking sunlight transmission through the water 

column, and increasing contaminant and nutrient concentrations. Report at 4-9 (citing P.J. Wood 

and P.D. Armitage, “Biological Effects of Fine Sediment in the Lotic Environment,” 

Environmental Management 21:203-217 (1997)). Over sedimentation thus can reduce 

photosynthesis and primary productivity within the stream network and otherwise have harmful 

effects on downstream biota, including on the health and abundance of fish, aquatic macrophytes 

(plants), and aquatic macroinvertebrates that inhabit downstream waters. See, e.g., Wood and 

Armitage 1997. Headwater streams tend to trap and store sediments behind large structures, such 
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as boulders and trees, that are transported downstream only during infrequent large storm events. 

See Report at 4-10, 4-12 (citing L.E. Benda, and T. W. Cundy, “Predicting deposition of debris 

flows in mountain channels,” Canadian Geotechnical Journal 27:409-417 (1990); T. Gomi and 

R. C. Sidle, “Bed load transport in managed steep-gradient headwater streams of southeastern 

Alaska,” Water Resources Research 39:1336 (2003); L.E. Benda, et al., “Geomorphology of 

steepland headwaters: The transition from hillslopes to channels,” Journal of the American 

Water Resources Association 41:835-851 (2005); P.E. Bigelow, et al., “On Debris Flows, River 

networks, and the Spatial Structure of Channel Morphology,” Forest Science 53:220-238 (2007);

J.P.R. Gooderham, et al., “Upstream Heterogeneous Zones: Small Stream Systems Structured by 

a Lack of Competence?” Journal of the North American Benthological Society 26:365-374 

(2007)).

Tributaries can greatly influence water temperatures in tributary networks. This is 

important because water temperature is a critical factor governing the distribution and growth of 

aquatic life, both directly (through its effects on organisms) and indirectly (through its effects on 

other physiochemical properties, such as dissolved oxygen and suspended solids). Id. at 4-13

(citing J.D. Allan, Stream Ecology – Structure and Function of Running Waters (New York, NY: 

Chapman & Hall, 1995)). For instance, water temperature controls metabolism and level of 

activity in cold-blooded species like fish, amphibians, and aquatic invertebrates. See, e.g., G.G. 

Ice, “Chapter 3: Stream Temperature and Dissolved Oxygen,” in J.D. Stednick, ed., Hydrologic

and Biological Responses to Forest Practices (Springer, 2008). Temperature can also control the 

amount of dissolved oxygen in streams, as colder water holds more dissolved oxygen, which fish 

and other fauna need to breathe. Connections between tributaries and downstream rivers can 

affect water temperature in river networks. See, e.g., Report at 4-13 (citing S. Knispel, and E. 
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Castella, “Disruption of a Longitudinal Pattern in Environmental Factors and Benthic Fauna by a 

Glacial Tributary,” Freshwater Biology 48:604-618 (2003); S.P. Rice, et al., “The Ecological 

Importance of Tributaries and Confluences,” in S.P. Rice, et al., ed., River Confluences, 

Tributaries and the Fluvial Network, (Chichester, UK: John Wiley & Sons, 2008), pp. 209-242)). 

In particular, tributaries provide both cold and warmwater refuge habitats that are critical for 

protecting aquatic life. Id. at 4-32. Because headwater tributaries often depend on groundwater 

inputs, temperatures in these systems tend to be warmer in the winter (when groundwater is 

warmer than ambient temperatures) and colder in the summer (when groundwater is colder than 

ambient temperatures) relative to downstream waters. Id. (citing G. Power, et al., “Groundwater 

and Fish: Insights from Northern North America,” Hydrological Processes 13:401-422 (1999)).

Thus tributaries provide organisms with both warmwater and coldwater refuges at different times 

of the year. Id. (citing R.A. Curry, et al., “Use of Small Streams by Young Brook Trout Spawned 

in a Lake,” Transactions of the American Fisheries Society 126:77-83 (1997); C.V. Baxter, and 

F.R. Hauer, “Geomorphology, Hyporheic Exchange and Selection of Spawning Habitat by Bull 

Trout (Salvelinus confluentus),” Canadian Journal of Fisheries and Aquatic Sciences 57: 1470-

1481 (2000); T.R. Labbe, and K. D. Fausch, “Dynamics of Intermittent Stream Habitat Regulate 

Persistence of a Threatened Fish at Multiple Scales,” Ecological Applications 10:1774-1791 

(2000); M.J. Bradford, et al., “Ecology of Juvenile Chinook Salmon in a Small Non-natal Stream 

of the Yukon River Drainage and the Role of Ice Conditions on Their Distribution and Survival,” 

Canadian Journal of Zoology-Revue Canadienne De Zoologie 79:2043-2054 (2001)). For 

example, when temperature conditions in downstream waters are adverse, fish can travel 

upstream and use tributaries as refuge habitat. Id. (citing Curry et al. 1997; M.A. Cairns, et al., 

“Influence of Summer Stream Temperatures on Black Spot Infestation of Juvenile Coho Salmon 
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in the Oregon Coast Range,” Transactions of the American Fisheries Society 134:1471-1479 

(2005)). Tributaries also help buffer temperatures in downstream waters. Id. at 4-13 to 4-14

(citing D. Caissie, “The thermal regime of rivers: A review,” Freshwater Biology 51:1389-1406

(2006). Temperatures in tributaries affect downstream water temperature many kilometers away. 

Id. at 4-14 (citing B. Gardner, and P.J. Sullivan, “Spatial and Temporal Stream Temperature 

Prediction: Modeling Nonstationary Temporal Covariance Structures,” Water Resources 

Research 40:W01102 doi (2004); B.R. Johnson, et al., “Use of Spatially Explicit 

Physicochemical Data to Measure Downstream Impacts of Headwater Stream Disturbance,” 

Water Resources Research 46:W09526 (2010)). 

D. Tributaries Significantly Affect the Chemical Integrity of (a)(1) through (a)(3) 

Waters

Tributaries transform and export significant amounts of nutrients and carbon to 

downstream waters, serving important source functions that greatly influence the chemical 

integrity of downstream waters. Organic carbon, in both dissolved and particulate forms, 

exported from tributaries is consumed by downstream organisms. The organic carbon that is 

exported downstream thus supports biological activity (including metabolism) throughout the 

river network. See, e.g., Report at 4-22 (citing S.G. Fisher and G.E. Likens, “Energy Flow in 

Bear Brook, New Hampshire: An Integrative Approach to Stream Ecosystem Metabolism,” 

Ecological Monographs 43: 421-439 (1973); J.L. Meyer, “The Microbial Loop in Flowing 

Waters,” Microbial Ecology 28:195-199 (1994); J.B. Wallace, et al. “Multiple Trophic Levels of 

a Forest Stream Linked to Terrestrial Litter Inputs,” Science 277:102-104 (1997); R.O. Hall and 

J.L. Meyer, “The Trophic Significance of Bacteria in a Detritus-Based Stream Food Web,” 

Ecology 79:1995-2012 (1998); R.O. Hall, et al., “Organic Matter Flow in Stream Food Webs 
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with Reduced Detrital Resource Base,” Ecology 81:3445-3463 (2000); C. Augspurger, et al.,

“Tracking Carbon Flow in a 2-Week-Old and 6-Week-Old Stream Biofilm Food Web,”

Limnology and Oceanography 53:642-650 (2008)). Much or most of the organic carbon that is 

exported from tributaries has been altered either physically or chemically by ecosystem 

processes within the tributary streams, particularly by headwater streams.

Nutrient export from tributaries has a large effect on downstream water quality, as excess 

nutrients from surface runoff from lawns and agricultural fields can cause algal blooms that 

reduce dissolved oxygen levels and increase turbidity in rivers, lakes, estuaries, and territorial 

seas. Water low in dissolved oxygen cannot support aquatic life; it is widely-recognized that this 

phenomenon has resulted in the devastation of commercial and recreational fisheries in the 

northern Gulf of Mexico. Committee on Environment and Natural Resources, Integrated 

Assessment of Hypoxia in the Northern Gulf of Mexico (Washington, D.C.: National Science and 

Technology Council, 2000). The amount of nitrogen that is exported downstream varies 

depending on stream size, and how much nitrogen is present in the system. Nitrogen loss is 

greater in smaller, shallow streams, most likely because denitrification and settling of nitrogen 

particles occur at slower rates in deeper channels. Report at 4-16 (citing R.G. Alexander, et al.,

“Effect of Stream Channel Size on the Delivery of Nitrogen to the Gulf of Mexico,” Nature

403:758-761(2000)). At low loading rates, the biotic removal of dissolved nitrogen from water is 

high and occurs primarily in small tributaries, reducing the loading to larger tributaries and rivers 

downstream. At high nitrogen loading rates, tributaries become nitrogen saturated and are not 

effectively able to remove nitrogen, resulting in high nitrogen export to rivers. Id. at 4-18 (citing 

P.J. Mulholland, et al., “Stream Denitrification across Biomes and Its Response to 

Anthropogenic Nitrate Loading,” Nature 452:202-205 (2008)). The transport of nitrogen and 
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phosphorus downstream has also been well-documented, particularly in the cases of the Gulf of 

Mexico and the Chesapeake Bay. Tributary streams in the uppermost portions of the Gulf and 

Bay watersheds transport the majority of nutrients to the downstream waters; an estimated 85% 

of nitrogen arriving at the hypoxic zone in the Gulf originates in the upper Mississippi (north of 

Cairo, Illinois) and the Ohio River Basins. D. Goolsby, et al., Topic Report 3, Flux and Sources 

of Nutrients in the Mississippi-Atchafalaya River Basin (Washington, D.C.: National Science and 

Technology Council Committee on Environment and Natural Resources, 1999). The export of 

nutrients from streams in the Mississippi River Basin has an effect on anoxia, or low oxygen 

levels, in the Gulf. Report at 4-17 (citing N.N. Rabalais, et al., “Gulf of Mexico Hypoxia, a.k.a. 

‘the Dead Zone,’” Annual Review of Ecology and Systematics 33:235-263 (2002)). Similarly, 

nutrient loads from virtually the entire 64,000 square mile watershed affect water quality in the 

Chesapeake Bay. Simulation tools have been used to determine the nutrient and sediment load 

reductions that must be made at many different points throughout the entire watershed in order to 

achieve acceptable water quality in the mainstem of the Bay. These reductions included specific 

annual nitrogen caps on the upper reaches of the Susquehanna River in New York State, more 

than 400 miles from the mouth of the Chesapeake Bay. See e.g., U.S. Environmental Protection 

Agency (EPA), Region III, Chesapeake Bay Program Office, Setting and Allocating the 

Chesapeake Bay Basin Nutrient and Sediment Loads: The Collaborative Process, Technical 

Tools and Innovative Approaches, EPA 903-R-03-007 (Washington, D.C.: EPA, 2003); Rabalais 

et al. 2002.

Although tributaries export nutrients, carbon, and contaminants downstream, they also 

transform these substances. Phosphorous and nitrogen arrive at downstream waters having 

already been cycled, or taken up and transformed by living organisms, many times in headwater 
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and smaller tributaries. Report at 4-19 to 4-20, 6-3 to 6-4 (citing J.R.Webster, and B.C. Patten, 

“Effects of watershed perturbation on stream potassium and calcium dynamics,” Ecological 

Monographs 49:51-72 (1979); J.D. Newbold, et al., “Measuring nutrient spiralling in streams,” 

Canadian Journal of Fisheries and Aquatic Sciences 38:860-863 (1981); J. Elwood, et al.,

“Resource spiraling: An operational paradigm for analyzing lotic ecosystems,” in T.D. Fontaine 

and S.M. Bartell, ed., Dynamics of Lotic Ecosystems (Ann Arbor, MI: Ann Arbor Science, 1983), 

pp. 3-23; S.H. Ensign, and M.W. Doyle, “Nutrient Spiraling in Streams and River Networks,” 

Journal of Geophysical Research-Biogeosciences 111:G04009 (2006)). In addition, some of the 

nutrient that is taken up as readily available inorganic forms is released back to the water as 

organic forms that are less available for biotic uptake. Id. at 4-20 (citing P.J. Mulholland, et al., 

“Production of Soluble, High Molecular Weight Phosphorus and Its Subsequent Uptake by 

Stream Detritus,” Verhandlungen des Internationalen Verein Limnologie 23:1190-1197 (1988); 

S.P. Seitzinger, et al., “Bioavailability of DON from Natural and Anthropogenic Sources to 

Estuarine Plankton,” Limnology and Oceanography 47:353-366 (2002)). Similarly, nutrient 

incorporated into particulates is not entirely regenerated, but accumulates in longitudinally 

increasing particulate loads (i.e. increases moving downstream). Id. at 4-20 (citing J.L Merriam, 

et al., “Characterizing Nitrogen Dynamics, Retention and Transport in a Tropical Rainforest 

Stream Using an in situ N-15 Addition,” Freshwater Biology 47:143-160 (2002); M.R. Whiles, 

and W.K. Dodds, “Relationships between Stream Size, Suspended Particles, and Filter-Feeding 

Macroinvertebrates in a Great Plains Drainage Network,” Journal of Environmental Quality

31:1589-1600 (2002); R.O. Hall, et al., “Hydrologic Control of Nitrogen Removal, Storage, and 

Export in a Mountain Stream,” Limnology and Oceanography 54:2128-2142 (2009)). Headwater 

streams have seasonal cycles in the concentrations of phosphorous and nitrogen that are 
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delivered downstream by accumulating nutrient derived from temporarily growing streambed 

biomass. Id. (citing P.J. Mulholland, and W.R. Hill, “Seasonal Patterns in Streamwater Nutrient 

and Dissolved Organic Carbon Concentrations: Separating Catchment Flow Path and In-Stream 

Effects,” Water Resources Research 33:1297-1306 (1997); P.J. Mulholland, “The Importance of 

In-stream Uptake for Regulating Stream Concentrations and Outputs of N and P from a Forested 

Watershed: Evidence from Long-Term Chemistry Records for Walker Branch Watershed,” 

Biogeochemistry 70:403-426 (2004)). Such variations have been demonstrated to affect 

downstream productivity. Id. (citing P.J. Mulholland, et al., “Longitudinal Patterns of Nutrient 

Cycling and Periphyton Characteristics in Streams: a Test of Upstream-Downstream Linkage,” 

Journal of the North American Benthological Society 14:357-370 (1995)). Nitrification, the 

microbial transformation of ammonium to nitrate, affects the form of downstream nutrient 

delivery. Nitrification occurs naturally in undisturbed headwater streams, but increases sharply in 

response to ammonium inputs, thereby reducing potential ammonium toxicity from pollutant 

inputs. Id. (citing Newbold, et al., “Phosphorus Dynamics in a Woodland Stream Ecosystem: a 

Study of Nutrient Spiralling,” Ecology 64:1249-1265 (1983); S.C. Chapra, Surface Water 

Quality Modeling (McGraw-Hill, 1996); E.S. Bernhardt, et al., “Whole-system Estimates of 

Nitrification and Nitrate Uptake in Streams of the Hubbard Brook Experimental Forest,” 

Ecosystems 5:419-430 (2002)). Denitrification, the removal of nitrate from streamwater through 

transformation to atmospheric nitrogen, is widespread among headwater streams; research 

indicates that small, unimpacted tributaries can reduce up to 40% of downstream nitrogen 

delivery through denitrification. Id. at 4-20 to 4-21 (citing P.J. Mulholland, et al., “Stream 

Denitrification across Biomes and Its Response to Anthropogenic Nitrate Loading,” Nature

452:202-205 (2008)). Small tributaries also affect the downstream delivery of nutrients through 
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abiotic processes. Streams can reduce phosphorus concentrations through sorption (i.e., 

“sticking”) to stream sediments. Id. at 4-21 (citing J.L. Meyer, “The Role of Sediments and 

Bryophytes in Phosphorus Dynamics in a Headwater Stream Ecosystem,” Limnology and 

Oceanography 24:365-375 (1979)). This is particularly beneficial to downstream chemical 

integrity where phosphorus sorbs to contaminants such as metal hydroxide precipitates. Id.

(citing J.A. Simmons, “Phosphorus Removal by Sediment in Streams Contaminated with Acid 

Mine Drainage,” Water Air and Soil Pollution 209:123-132 (2010)).

Tributaries also store significant amounts of nutrients and carbon, functioning as 

important sinks (lags) for river networks so that they do not reach downstream traditional 

navigable waters, interstate waters, or tributary streams. Small tributary streams in particular 

often have the greatest effect on downstream water quality, in terms of storage and reducing 

inputs to downstream waters. For instance, uptake and transformation of inorganic nitrogen often 

occurs most rapidly in the smallest tributaries. See, e.g., id. at 4-18 (citing B.J. Peterson, et al., 

“Control of Nitrogen Export from Watersheds by Headwater Streams,” Science 292: 86-90 

(2001)). Small tributaries affect the downstream delivery of nutrients such as phosphorus 

through abiotic processes; such streams can reduce phosphorus concentrations by sorption to 

stream sediments. 

Tributaries can also serve as a temporary or permanent source or sink for contaminants, 

for instance substances like metals, sodium, and even dead fish carcasses that adversely affect 

organisms when occurring at excessive or elevated concentrations to reduce the amounts that 

reach downstream traditional navigable waters, interstate waters, or tributary streams. The 

transport of contaminants to downstream waters can impact water quality downstream, if they 

are not stored in tributaries. See, e.g., id. at 4-26 (citing X. Wang, et al., “Water Quality Changes 
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as a Result of Coalbed Methane Development in a Rocky Mountain Watershed,” Journal of the 

American Water Resources Association 43:1383-1399 (2007)). Tributaries can also serve as at 

least a temporary sink for contaminants that would otherwise impair downstream water quality. 

See, e.g., id. at 133-134 (citing W.L. Graf, Plutonium and the Rio Grande: Environmental 

Change and Contamination in the Nuclear Age (New York: Oxford University Press, 1994)).

The distances and extent of metal contaminant transport was shown in separate studies in 

the upper Arkansas River in Colorado, and Clark Fork River in Montana, where past mining 

activities impacted the headwater tributaries. River bed sediments showed that metals originating 

from the mining and smelting areas in the headwaters were reaching water bodies up to 550 km 

downstream. Id. at 4-26 to 4-27 (citing E.V. Axtmann, and S.N. Luoma, “Large-scale 

Distribution of Metal Contamination in the Fine-grained Sediments of the Clark Fork River, 

Montana, USA,” Applied Geochemistry 6:75-88 (1991); B.A. Kimball, et al., “Effects of 

Colloids on Metal Transport in a River Receiving Acid Mine Drainage, Upper Arkansas River, 

Colorado, USA,” Applied Geochemistry 10:285-306 (1995)).

Military studies of the distribution, transport, and storage of radionuclides (e.g., 

plutonium, thorium, uranium) have provided convincing evidence for distant chemical 

connectivity in river networks because the natural occurrence of radionuclides is extremely rare. 

From 1942 to 1952, prior to the full understanding of the risks of radionuclides to human health 

and the environment, plutonium dissolved in acid was discharged untreated into several 

intermittent headwater streams that flows into the Rio Grande at the Los Alamos National 

Laboratory, New Mexico. Id. at 4-28 (citing W.L. Graf, Plutonium and the Rio Grande: 

Environmental Change and Contamination in the Nuclear Age (New York: Oxford University 

Press, 1994); S.L. Reneau, et al., “Geomorphic Controls on Contaminant Distribution along an 
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Ephemeral Stream,” Earth Surface Processes and Landforms 29:1209-1223 (2004)). Also 

during this time, nuclear weapons testing occurred west of the upper Rio Grande near Socorro, 

New Mexico (Trinity blast site) and in Nevada, where fallout occurred on mountainous areas 

with thin soils that are readily transported to headwater streams in the upper Rio Grande basin. 

The distribution of plutonium within the Rio Grande illustrates how headwater streams transport 

and store contaminated sediment that has entered the basin through fallout and from direct 

discharge. Los Alamos Canyon, while only representing 0.4% of the drainage area at its 

confluence with the Rio Grande, had a mean annual bedload contribution of plutonium almost 

seven times that of the mainstem. Id. (citing Graf 1994). Much of the bedload contribution 

occurred sporadically during intense storms that were out of phase with flooding on the upper 

Rio Grande. Total estimated contributions of plutonium between the two sources to the Rio 

Grande were approximately ~90% from fallout to the landscape and 10% from direct effluent 

discharge at Los Alamos National Laboratory. Id. (citing Graf 1994). 

E. Tributaries Significantly Affect the Biological Integrity of (a)(1) through (a)(3) 

Waters

Tributaries are biologically linked to downstream waters through the movement of living 

organisms or their reproductive propagules, such as eggs or seeds. For organisms that drift with 

water flow, biological connections depend on hydrological connections. However, many aquatic 

organisms are capable of active movement with or against water flow, and others disperse 

actively or passively over land by walking, flying, drifting, or “hitchhiking.” All of these 

different types of movement form the basis of biological connectivity between headwater 

tributaries and downstream waters.
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Headwater tributaries increase the amount and quality of habitat available to aquatic 

organisms. Under adverse conditions, small tributaries provide safe refuge, allowing organisms 

to persist and recolonize downstream areas once adverse conditions have abated. See, e.g., 

Report at 4-29 (citing J.L. Meyer and J.B. Wallace, “Lost Linkages and Lotic Ecology: 

Rediscovering Small Streams,” Pages 295-317 in M. C. Press, N. J. Huntly, and S. Levin, 

editors. Ecology: Achievement and Challenge (Oxford, UK: Blackwell Science, 2001); A. Meyer 

et al., “The Effect of Low Flow and Stream Drying on the Distribution and Relative Abundance 

of the Alien Amphipod, Echinogammarus berilloni (Catta, 1878) in a Karstic Stream System 

(Westphalia, Germany),” Crustaceana 77:909-922 (2004); A.D. Huryn et al., “Landscape 

Heterogeneity and the Biodiversity of Arctic Stream Communities: A Habitat Template 

Analysis,” Canadian Journal of Fisheries and Aquatic Sciences 62:1905-1919 (2005)). Use of 

tributaries by salmon and other anadramous fish for spawning is well-documented, but even nonmigratory species can travel great distances within the river and tributary networks. See, e.g., id.

at 4-31 (citing O.T. Gorman, “Assemblage Organization of Stream Fishes: The Effects of Rivers 

on Adventitious Streams,” American Naturalist 128(4): 611-616 (1986); A. L. Sheldon, 

“Conservation of Stream Fishes: Patterns of Diversity, Rarity, and Risk,” Conservation Biology

2:149-156 (1988); N.P. Hitt and P.L. Angermeier, “Evidence for Fish Dispersal from Spatial 

Analysis of Stream Network Topology,” Journal of the North American Benthological Society 

27:304-320 (2008)). Tributaries also serve as an important source of food for biota in 

downstream rivers. Tributaries export plankton, vegetation, fish eggs, insects, invertebrates like 

worms or crayfish, smaller fish that originate in upstream tributaries and other food sources that 

drift downstream to be consumed by other animals. See, e.g., id. at 4-29 (citing D.J. Progar and 

A.R. Modenke, “Insect Production from Temporary and Perennially Flowing Headwater Streams 
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in Western Oregon,” Journal of Freshwater Ecology 17:391-407 (2002)). For example, many 

fish feed on drifting insects, and numerous studies document the downstream drift of stream 

invertebrates that then are eaten by fish in larger rivers. See, e.g., id. at 4-29 to 4-30 (citing S. 

Nakano and M. Murakami, “Reciprocal Subsidies: Dynamic Interdependence between 

Terrestrial and Aquatic Food Webs,” Proceedings of the National Academy of Sciences USA

98:166-170 (2001); M.S. Wipfli and D.P. Gregovich, “Export of Invertebrates and Detritus from 

Fishless Headwater Streams in Southeastern Alaska: Implications for Downstream Salmonid 

Production,” Freshwater Biology 47:957-969 (2002)).

Biological connectivity also allows gene flow, or genetic connectivity, among tributary 

and river populations. Gene flow is needed to maintain genetic diversity in a species, a basic 

requirement for that species to be able to adapt to environmental change. Populations connected 

by gene flow have a larger breeding population size, making them less prone to the deleterious 

effects of inbreeding and local extinction. Id. at 4-33 (citing R. Lande and S. Shannon, “The role 

of genetic variation in adaptation and population persistence in a changing environment,” 

Evolution 50:434-437 (1996)). Genetic connectivity exists at multiple scales and can extend 

beyond one a single river catchment, and for species capable of long distance movement (such as 

salmon), reveals complex interactions among spatially distant populations of aquatic organisms 

Id. (citing J. M. Hughes, et al., “Genes in Streams: Using DNA to Understand the Movement of 

Freshwater Fauna and Their Riverine Habitat,”Bioscience 59:573-583 (2009); C.D. Anderson, 

“Considering spatial and temporal scale in landscape-genetic studies of gene flow,” Molecular 

Ecology 19:3565-3575 (2010)).

F. Headwater Tributaries Significantly Affect the Chemical, Physical, and Biological 

Integrity of (a)(1) through (a)(3) Waters
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As discussed above, the scientific literature supports the conclusion that tributaries, 

including headwater streams, have a significant nexus to downstream waters based on their 

contribution to the chemical, physical, and biological integrity of (a)(1) through (a)(3) waters. 

Headwater tributaries, the small streams at the uppermost reaches of the tributary network, are 

the most abundant streams in the United States. See, e.g., id. at 4-2 (citing T.L. Nadeau and M.C. 

Rains, “Hydrological connectivity between headwater streams and downstream waters: How 

science can inform policy,” Journal of the American Water Resources Association 43:118-133

(2007))Collectively, they help shape the chemical, physical, and biological integrity of 

downstream waters, and provide many of the same functions as non-headwater streams. See, 

e.g., id. at 1-7 to 1-8, 4-1. For example, headwater streams reduce the amount of sediment 

delivered to downstream waters by trapping sediment from water and runoff. See, e.g., M. 

Dieterich and N.H. Anderson, “Dynamics of Abiotic Parameters, Solute Removal and Sediment 

Retention in Summer-Dry Headwater Stream of Western Oregon,” Hydrobiologia 379: 1-15 

(1998). Headwater streams shape river channels by accumulating and gradually or episodically 

releasing sediment and large woody debris into river channels. They are also responsible for 

most nutrient cycling and removal, and thus transforming and changing the amount of nutrients 

delivered to downstream waters. See, e.g., Report at 4-18 (citing B.J. Peterson, et al., “Control of 

Nitrogen Export from Watersheds by Headwater Streams,” Science 292: 86-90 (2001)). A close 

connection exists between the water quality of these streams and the water quality of TNWs, IW, 

and TS. See, e.g., State of Ohio Environmental Protection Agency, Nonpoint Source Impacts on 

Primary Headwater Streams (Columbus, OH: Ohio Environmental Protection Agency, 2003). 

Activities such as discharging a pollutant into one part of the tributary system are welldocumented to affect other parts of the system, even when the point of discharge is far upstream 
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from the navigable water that experiences the effect of the discharge. See, e.g., F.M. Dunnivant 

and E. Anders, A Basic Introduction To Pollutant Fate and Transport: An Integrated Approach 

With Chemistry, Modeling, Risk Assessment, and Environmental Legislation (Hoboken, NJ: John 

Wiley & Sons, Inc., 2006). 

Headwater streams provide unique habitat and protection for amphibians, fish, and other 

aquatic or semi-aquatic species living in and near the stream that may use the downstream waters 

for other portions of their life stages. See, e.g., Report at 1-8; J.L. Meyer, et al., “The 

Contribution of Headwater Streams to Biodiversity in River Networks,” Journal of the American 

Water Resources Association 43(1): 86-103 (2007). They also serve as migratory corridors for 

fish. Tributaries can improve or maintain biological integrity and can control water temperatures 

in the downstream waters. See, e.g., Report at 4-14 (citing J.L. Ebersole, et. al., “Cold water 

patches in warm streams: Physicochemical characteristics and the influence of shading,” Journal 

of the American Water Resources Association 39:355-368 (2003); B. Gardner, and P.J. Sullivan, 

“Spatial and temporal stream temperature prediction: Modeling nonstationary temporal 

covariance structures,” Water Resources Research 40:1-9 (2004); B.R. Johnson, et al., “Use of 

spatially explicit physicochemical data to measure downstream impacts of headwater stream 

disturbance,” Water Resources Research 46:W09526 (2010)). Headwater streams also provide 

refuge habitat for riverine organisms seeking protection from temperature extremes, flow 

extremes, low dissolved oxygen, high sediment levels, or the presence of predators, parasites, 

and competitors. See, e.g., id. at 4-32 (citing J.C. Scrivener, et al., “Juvenile Chinook salmon 

(Oncorhynchus tshawytscha) utilization of Hawks Creek, a small and nonnatal tributary of the 

Upper Fraser River,” Canadian Journal of Fisheries and Aquatic Sciences 51:1139-1146 (1994); 

R.A. Curry, et al., “Use of small streams by young brook trout spawned in a lake,” Transactions 
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of the American Fisheries Society 126:77-83 (1997); A.M. Pires, et al., “Seasonal changes in fish 

community structure of intermittent streams in the middle reaches of the Guadiana basin, 

Portugal,” Journal of Fish Biology 54:235-249 (1999); M.J Bradford, et al., “Ecology of juvenile 

Chinook salmon in a small nonnatal stream of the Yukon River drainage and the role of ice 

conditions on their distribution and survival,” Canadian Journal of Zoology-Revue Canadienne 

De Zoologie 79:2043-2054 (2001); M.A. Cairns, et al., “Influence of summer stream 

temperatures on black spot infestation of juvenile coho salmon in the Oregon Coast Range,” 

Transactions of the American Fisheries Society 134:1471-1479 (2005); Wigington, P. J., et al., 

“Coho salmon dependence on intermittent streams,” Frontiers in Ecology and the Environment

4:513-518 (2006)). Headwater streams serve as a source of food materials such as insects, larvae, 

and organic matter to nourish the fish, mammals, amphibians, and other organisms in 

downstream streams, rivers, and lakes. See, e.g., id. at 4-22, 4-24 (citing S.G., Fisher, and G. E. 

Likens, “Energy flow in Bear Brook, New Hampshire: An integrative approach to stream 

ecosystem metabolism,” Ecological Monographs 43:421-439 (1973); J.L. Meyer, “The microbial 

loop in flowing waters,” Microbial Ecology 28:195-199 (1994); J.B. Wallace, et al., “Multiple 

trophic levels of a forest stream linked to terrestrial litter inputs,” Science 277:102-104 (1997); 

R.O. Hall, and J.L. Meyer, “The trophic significance of bacteria in a detritus-based stream food 

web,” Ecology 79:1995-2012 (1998); R.O. Hall, et al., “Organic matter flow in stream food webs 

with reduced detrital resource base,” Ecology 81:3445-3463 (2000); T. Gomi, et al., 

“Understanding processes and downstream linkages of headwater systems,” Bioscience 52:905-

916 (2002); C. Augspurger, et al., “Tracking carbon flow in a 2-week-old and 6-week-old stream 

biofilm food web,” Limnology and Oceanography 53:642-650 (2008)). Disruptions in these 

biological processes affect the ecological functions of the entire downstream system. See, e.g., 
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L.A. Kaplan, et al., “Patterns of Dissolved Organic Carbon in Transport,” Limnology and 

Oceanography 25: 1034-1043 (1980); R.L. Vannote, et. al., “The River Continuum Concept,”

Canadian Journal of Fisheries and Aquatic Sciences 37: 130-37 (1980). Headwater streams can 

help to maintain base flow in the larger rivers downstream, which is particularly important in 

times of drought. See, e.g., Report at 4-4, 4-66 (citing P.D. Brooks, and M.M. Lemon, “Spatial 

variability in dissolved organic matter and inorganic nitrogen concentrations in a semiarid 

stream, San Pedro River, Arizona,” Journal of Geophysical Research-Biogeosciences

112:G03S05.D (2007); Tetzlaff, and C. Soulsby, “Sources of baseflow in larger catchments –

using tracers to develop a holistic understanding of runoff generation,” Journal of Hydrology

359:287-302 (2008)). At the same time, the network of headwater streams can regulate the flow 

of water into downstream waters, mitigating low flow and high flow extremes, reducing local 

and downstream flooding, and preventing excess erosion caused by flooding. See, e.g., United 

States, U.S. EPA and USDA/ARS Southwest Watershed Research Center, EPA/600/R-08/134, 

ARS/2330462008: The Ecological and Hydrological Significance of Ephemeral and Intermittent 

Streams in the Arid and Semi-arid American Southwest (Washington, D.C.: U.S. EPA and 

USDA/ARS Southwest Watershed Research Center, Levick et al., 2008) (Levick et al. 2008).

Tributaries do not need to flow perennially to have a significant nexus to downstream 

waters. Approximately 59% of streams across the United States (excluding Alaska) flow 

intermittently or ephemerally; ephemeral and intermittent streams are particularly prevalent in 

the arid and semi-arid Southwest, where they account for over 81% of streams. Levick et al. 

2008. Despite their intermittent or ephemeral flow, these streams nonetheless perform the same 

important ecological and hydrological functions documented in the scientific literature as 

perennial streams, through their movement of water, nutrients, and sediment to downstream 
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waters. Id. The importance of intermittent and ephemeral streams is documented in a 2008 peerreviewed report by EPA’s Office of Research and Development and the U.S. Department of 

Agriculture’s Agricultural Research Service, which addresses the hydrological and ecological 

significance of ephemeral and intermittent streams in the arid and semi-arid Southwestern United 

States and their connections to downstream waters; the report is a state-of-the-art synthesis of 

current knowledge of the ecology and hydrology in these systems. Id.

Intermittent and ephemeral streams are chemically, physically, and biologically 

connected to downstream waters, and these connections have effects downstream. See, e.g., id. In 

some areas, stormflows channeled into alluvial floodplain aquifers by intermittent and ephemeral 

streams are the major source of annual streamflow in rivers. Perennial flows are not necessary 

for chemical connections. Periodic flows in ephemeral or intermittent tributaries can have a 

strong influence on biogeochemistry by connecting the channel and other landscape elements. 

See, e.g., Report at 4-16 (citing H.M. Valett, et. al., “Biogeochemical and Metabolic Responses 

to the Flood Pulse in a Semiarid Floodplain,” Ecology 86(1): 220-234 (2005)). This episodic 

connection can be very important for transmitting a substantial amount of material into 

downstream rivers. See, e.g., id. (citing Nadeau and Rains (2007)). Ephemeral desert streams 

have been shown to export particularly high sediment loadings. See, e.g., id. at 4-10 (citing M.A. 

Hassan, “Observations of Desert Food Bores,” Earth Surface Processes and Landforms 15:481-

485 (1990)). Ephemeral streams can also temporarily and effectively store large amounts of 

sediment that would otherwise wash downstream, contributing to the maintenance of 

downstream water quality and productive fish habitat. See, e.g., S.H. Duncan, et al., “Transport 

of Road-Surface Sediment through Ephemeral Stream Channels,” Water Resources Bulletin
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23(1): 113-119 (1987). This temporary storage of sediment thus helps maintain the chemical and 

biologic integrity of downstream waters.

The Report provides case studies of prairie streams and Southwest intermittent and 

ephemeral streams, two stream types whose jurisdictional status has been called into question in 

the past. These case studies highlight the importance of these streams to downstream waters, 

despite their small size and ephemeral or intermittent flow regime. Prairie streams are frequently 

subjected to the extremes of drying and flooding, and intermittent or flashy hydrology is 

prevalent in river networks throughout most of the Great Plains. Report at 4-40 (citing W.J. 

Matthews, “North American Prairie Streams as Systems for Ecological Study,” Journal of the 

North American Benthological Society 7:387-409 (1988); A.V. Zale et al., “The 

Physicochemistry, Flora, and Fauna of Intermittent Prairie Streams: A Review of the Literature,”

United States Fish and Wildlife Service Biological Report 89:1-44 (1989); N.L. Poff, “A 

Hydrogeography of Unregulated Streams in the United States and an Examination of Scale 

Dependence in Some Hydrological Descriptors,” Freshwater Biology 36:71-91 (1996); W.K. 

Dodds, et al., “Life on the Edge: The Ecology of Great Plains Prairie Streams,” Bioscience

54:205-216 (2004)). Prairie streams typically represent a collection of spring-fed, perennial pools 

and reaches, embedded within larger, intermittently flowing segments. Id. at 4-55 (citing T.R. 

Labbe, and K.D. Fausch, “Dynamics of Intermittent Stream Habitat Regulate Persistence of a 

Threatened Fish at Multiple Scales,” Ecological Applications 10:1774-1791 (2000)). These 

streams have significant chemical, physical, and biological connections to downstream waters, 

despite extensive alteration of historical prairie regions by agriculture, water impoundment, 

water withdrawals, and other human activities, and the challenges these alterations create for 

assessing connectivity. Id. (citing W.J. Matthews, and H.W. Robinson, “Influence of Drainage 
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Connectivity, Drainage Area and Regional Species Richness on Fishes of the Interior Highlands 

in Arkansas,” American Midland Naturalist 139:1-19 (1998); W.K. Dodds, et al., “Life on the 

Edge: the Ecology of Great Plains Prairie Streams,” Bioscience 54:205-216 (2004)). The most 

notable connections are via flood propagation, contaminated sediment transport, nutrient 

retention, and the extensive transport and movement of fish species (including eggs and larvae) 

throughout these networks. Id. at 4-55 (citing H.F. Matthai, Floods of June 1965 in South Platte 

River Basin, Colorado, Water Supply Paper 1850-B (Washington, D.C.: U.S. Geological Survey, 

1969); A.J. Horowitz, et al., “The Effect of Mining on the Sediment-trace Element Geochemistry 

of Cores from the Cheyenne River Arm of Lake Oahe, South Dakota, USA,” Chemical Geology

67:17-33 (1988); D.C. Marron, “The Transport of Mine Tailings as Suspended Sediment in the 

Belle Fourche River, West-central South Dakota, USA,” International Association of Hydrologic 

Sciences 184:19-26 (1989); W.K. Dodds, et al., “Nitrogen Transport from Tallgrass Prairie 

Watersheds,” Journal of Environmental Quality 25:973-981 (1996a); K.D. Fausch, and K.R. 

Bestgen, “Ecology of Fishes Indigenous to the Central and Southwestern Great Plains,” in F.L. 

Knopf and F.B. Samson, ed., Ecology and Conservation of Great Plains Vertebrates, (New 

York, NY: Springer-Verlag, 1997), pp. 131-166; S.P. Platania, and C.S. Altenbach, 

“Reproductive Strategies and Egg Types of Seven Rio Grande Basin Cyprinids,” Copeia

1998:559-569 (1998); K.M. Fritz, and W.K. Dodds, “Resistance and Resilience of 

Macroinvertebrate Assemblages to Drying and Flood in a Tallgrass Prairie Stream System,” 

Hydrobiologia 527:99-112 (2004); K.M. Fritz, and W.K. Dodds, “Harshness: Characterization of 

Intermittent Stream Habitat over Space and Time,” Marine and Freshwater Research 56:13-23 

(2005); N.R. Franssen, et al., “Effects of Floods on Fish Assemblages in an Intermittent Prairie 

Stream,” Freshwater Biology 51:2072-2086 (2006); R.B. Alexander, et al., “Differences in 
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Phosphorus and Nitrogen Delivery to the Gulf of Mexico from the Mississippi River Basin,” 

Environmental Science & Technology 42:822-830 (2008); J.S. Perkins, and K.B. Gido, “Stream 

Fragmentation Thresholds for a Reproductive Guild of Great Plains Fishes,” Fisheries 36:371-

383 (2011)). 

Southwestern intermittent and ephemeral streams exert strong influences on the structure 

and function of downstream waters, and the case study (included in the Report) echoes many of 

the findings of the functions of intermittent and ephemeral tributaries generally, which are 

described above. The case study focuses on the heavily studied San Pedro River, located in 

southeast Arizona, in particular, as a representative example of the hydrological behavior and the 

connectivity of rivers in the Southwest, but also examines evidence relevant to other 

Southwestern streams. The chemical, physical, and biological connections of Southwestern 

intermittent and ephemeral streams highlighted in the case study are summarized below. Flows 

from ephemeral streams are one of the major drivers of the dynamic hydrology of Southwest 

rivers (particularly of floods during monsoon seasons. Id. at 4-60, 4-67 (citing D.C. Goodrich, et 

al., “Linearity of Basin Response as a Function of Scale in a Semiarid Watershed,” Water 

Resources Research 33:2951-2965 (1997); F. Yuan, and S. Miyamoto, “Characteristics of 

Oxygen-18 and Deuterium Composition in Waters from the Pecos River in American 

Southwest,” Chemical Geology 255:220-230 (2008)). Downstream river fishes and invertebrates 

are adapted to the variable flow regimes that are influenced strongly by ephemeral tributary 

systems, which provide isolated pools as refuges for fish during dry periods. Id. at 4-68 to 4-69

(citing K.R. John, “Survival of Fish in Intermittent Streams of the Chirichua Mountains, 

Arizona” Ecology 45:112-119 (1964); T.R. Labbe, and K.D. Fausch, “Dynamics of Intermittent 

Stream Habitat Regulate Persistence of a Threatened Fish at Multiple Scales,” Ecological 
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Applications 10:1774-1791 (2000); J.N. Rinne, and D. Miller, “Hydrology, Geomorphology and 

Management: Implications for Sustainability of Native Southwestern Fishes,” Reviews in 

Fisheries Science 14:91-110 (2006); D.A. Lytle, et al., “Evolution of Aquatic Insect Behaviors 

across a Gradient of Disturbance Predictability,” Proceedings of the Royal Society - Series B

275:453-462 (2008)). Ephemeral tributaries in the Southwest also supply water to mainstem river 

alluvial aquifers, which aids in the sustaining river baseflows downstream. Id. at 4-64 (citing 

D.C. Goodrich, et al., “Linearity of Basin Response as a Function of Scale in a Semiarid 

Watershed,” Water Resources Research 33:2951-2965 (1997); J.B. Callegary, et al., “Rapid 

Estimation of Recharge Potential in Ephemeral-Stream Channels using Electromagnetic 

Methods, and Measurements of Channel and Vegetation Characteristics,” Journal of Hydrology

344:17-31 (2007)). Ephemeral tributaries export sediment downstream during major hydrologic 

events; the sediment, in turn, contributes to materials that comprise alluvial aquifers and shape 

the fluvial geomorphology (the science of how rivers and streams form given the landscape 

setting) of downstream waters. Id. at 4-65 (citing G.C. Nanson, and J.C. Croke, “A Genetic 

Classification of Floodplains,” Geomorphology 4:459-486 (1992)). The nutrient and 

biogeochemical integrity of downstream Southwestern rivers, such as the San Pedro River, is 

heavily influenced by nutrient export from ephemeral tributaries after storm flow events. Id. at 4-

18, 4-66 (citing P.D. Brooks, and M.M. Lemon, “Spatial Variability in Dissolved Organic Matter 

and Inorganic Nitrogen Concentrations in a Semiarid Stream, San Pedro River, Arizona,” 

Journal of Geophysical Research-Biogeosciences 112:G03S05 (2007)). Extensive downstream 

river riparian communities are supported by water, sediment and nutrients exported to the river 

from ephemeral tributaries; these riparian communities have a profound influence on the river 

attributes through shading, allochthonous (originating from outside of the channel) inputs of 
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organic matter, detritus, wood, and invertebrates to the river. Id. at 4-65 to 4-66 (citing S.V. 

Gregory, et al., “An Ecosystem Perspective of Riparian Zones: Focus on Links between Land 

and Water,” Bioscience 41:540-551 (1991); R.J. Naiman, et al., Riparia: Ecology, Conservation, 

and Management of Streamside Communities (Burlington, MA: Elsevier, Inc., 2005); J.C. 

Stromberg, et al., “Effects of Stream Flow Intermittency on Riparian Vegetation of a Semiarid 

Region River (San Pedro River, Arizona),” River Research and Applications 21:925-938 (2005), 

M. Baillie, et al., “Quantifying Water Sources to a Semiarid Riparian Ecosystem, San Pedro 

River, Arizona,” Journal of Geophysical Research 112:G03S02 (2007); National Research 

Council, Riparian Areas: Functions and Strategies for Management (Washington, D.C.: 

National Academy Press, 2002)). 

G. Tributary Lakes, Ponds, and Wetlands Significantly Affect the Chemical, Physical, 

and Biological Integrity of (a)(1) through (a)(3) Waters

As discussed elsewhere in this preamble, riparian and floodplain wetlands have a 

significant nexus to downstream waters, and wetlands that are tributaries are a subset of such 

wetlands. The fact that a wetland tributary is in-stream often enhances its ability to filter 

pollutants and contaminants that would otherwise make it downstream; in-stream wetlands also 

attenuate floodwaters. Lakes and ponds serve many important functions that affect the chemical, 

physical, and biological conditions downstream. Lake tributaries can act as sinks, storing 

floodwaters, sediment, and nutrients, as these materials have the opportunity to settle out, at least 

temporarily, as water moves through the lake to downstream waters. See, e.g., R.W. Phillips, et 

al., “Connectivity and Runoff Dynamics in Heterogeneous Basins,” Hydrological Processes

25(19): 3061-3075 (2011). The attenuation of floodwaters can also maintain stream flows 

downstream. Id. Lakes, as with other tributaries, can also act as sources, contributing flow, 
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nutrient, sediment, and other materials downstream. Total Maximum Daily Loads (TMDLs) for 

nutrients have been established for many in-stream lakes across the country in recognition of the 

ability of lakes to transport nutrients downstream, contributing to downstream impairments. See, 

e.g. Maine Department of Environmental Protection, Phosphorus Control Action Plan and Total 

Maximum Daily (Annual Phosphorous) Load Report, Daigle Pond, New Canada, Aroostook 

County, Maine, Daigle Pond PCAP – TMDL Report, Maine DEPLW – 0789 (Maine DEP, 

2006); U.S. Environmental Protection Agency, “Section 6 Echo Park Lake TMDLs,” Los 

Angeles Area Lakes TMDLs, January 2011 Revised Draft (2011). Lakes can also serve as habitat 

for species that then move downstream. For instance, brook trout that are stocked in headwater 

lakes in Idaho and Montana are capable of invading most downstream habitat, including through 

very steep channel slopes and waterfalls. S.B. Adams, et al., “Geography of Invasion in 

Mountain Streams: Consequences of Headwater Lake Fish Introductions,” Ecosystems 4(4): 

296-307. These non-native species can then affect the biological integrity of downstream waters 

by impacting populations of native fish species, such as cutthroat trout, downstream. See, e.g., 

J.B. Dunham, et al., “Alien Invasions in Aquatic Ecosystems: Toward an Understanding of 

Brook Trout Invasions and Potential Impacts on Inland Cutthroat Trout in Western North 

America,” Reviews in Fish Biology and Fisheries 12(4): 373-391 (2002). For example, nonnative trout were introduced in headwater tributary lakes to the Little Kern River in the southern 

Sierra Nevada and dispersed downstream, causing the near-extinction of the native Little Kern 

golden trout. R.A. Knapp, and K.R. Matthews, “Effects on Nonnative Fishes on Wilderness Lake 

Ecosystems in the Sierra Nevada and Recommendations for Reducing Impacts,” in D. N. Cole, et 

al., ed., Wilderness Science in a Time of Change Conference, Volume 5: Wilderness Ecosystems, 

Threats, and Management, Missoula, Montana, May 23-27, 1999, Proceedings RMRS-P-15-
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VOL-5 (Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station, 2000), 312-317. These studies demonstrate the ability of organisms to travel from 

tributary lakes to downstream waters, which is not limited to just non-native species; many other 

species can also move downstream and back again. 

One type of wetlands located in-stream are unidirectional wetlands that are connected to 

the river network through a channel (e.g., wetlands that serve as stream origins; a definition of 

“unidirectional wetlands” can be found in part I section 4.B above). These tributary wetlands are 

generally exemplary of tributary wetlands as a whole, and because the Report focuses in part on 

these wetlands, they are discussed here in further detail. These are wetlands from which a stream 

channel originates. Report at 5-1 to 5-2. They are part of the stream network itself, and along 

with first- and second-order streams, form the headwaters of the river network. Such wetlands 

have a direct hydrologic connection to the tributary network via unidirectional flow from 

wetland to the headwater stream. Channel origin wetlands generally have important chemical, 

physical, and biological effects on (a)(1) through (a)(3) waters, including hydrologic, water 

quality, and habitat functions, regardless if the outflow from the wetland to the stream is 

perennial, intermittent, or ephemeral. Id. Like other wetlands, wetlands that serve as stream 

origins can transport channel-forming sediment and woody debris, transport stored organic 

matter, remove and transform pollutants and excess nutrients such as nitrogen and phosphorus, 

attenuate and store floodwaters, contribute to stream baseflow through groundwater recharge, 

and provide habitat for breeding fish, amphibians, reptiles, birds, and other aquatic and semiaquatic species that move from the wetlands to the river network. Id. at 5-41.

Wetlands that serve as stream origins connect via perennial, intermittent, or ephemeral 

drainages to river networks. Id. at 5-22 to 5-23 (citing M.C. Rains, et al., “The Role of Perched 
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Aquifers in Hydrological Connectivity and Biogeochemical Processes in Vernal Pool 

Landscapes, Central Valley, California,” Hydrological Processes 20:1157-1175 (2006); M.C. 

Rains, et al., “Geological Control of Physical and Chemical Hydrology in California Vernal 

Pools,” Wetlands 28:347-362 (2008); T.R. Morley, et al., “The Role of Headwater Wetlands in 

Altering Streamflow and Chemistry in a Maine, USA Catchment,” Journal of the American 

Water Resources Association 47:337-349 (2011)). Regardless of the permanence of flow, such 

wetlands have an impact on downstream water. Id. at 5-1 to 5-2. Wetland seeps, for example, can 

form where groundwater discharges from breaks in slope. Id. at 5-21 (citing B.R. Hall, et al., 

“Environmental Influences on Plant Species Composition in Ground-water Seeps in the Catskill 

Mountains of New York,” Wetlands 21:125-134 (2001); M.A. O’Driscoll, and D.R. DeWalle, 

“Seeps Regulate Stream Nitrate Concentration in a Forested Appalachian Catchment,” Journal of 

Environmental Quality 39:420-431 (2010)). They often have perennial connections to the stream, 

providing important sources of water downstream, particularly during summer baseflow. Id. at 5-

22 (citing T.R. Morley, et al., “The Role of Headwater Wetlands in Altering Streamflow and 

Chemistry in a Maine, USA Catchment,” Journal of the American Water Resources Association

47:337-349 (2011)). In Maine, for example, seeps were found to provide 40 to 80% of stream 

water during baseflow periods. Id. In other cases, surface connections between channel origin 

wetlands and streams are intermittent or ephemeral. For example, California vernal pools spill 

water a great number of days during the years via channels, providing water downstream. Id. 

(citing M.C. Rains, et al., “The Role of Perched Aquifers in Hydrological Connectivity and 

Biogeochemical Processes in Vernal Pool Landscapes, Central Valley, California,” Hydrological 

Processes 20:1157-1175 (2006); M.C. Rains, et al., “Geological Control of Physical and 

Chemical Hydrology in California Vernal Pools,” Wetlands 28:347-362 (2008)). In addition to 
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surface water connections, groundwater flow can wetlands that serve as stream origins with the 

stream network. Id. at 5-23. 

The hydrologic connection of the wetland to the stream can affect streamflow by altering

baseflow or storm flow through several mechanisms, including surface storage and groundwater 

recharge. Id. at 5-25. Studies at the larger scale have shown that wetlands, by storing water, 

reduce peak streamflows and, thus, downstream flooding. Id. (citing J. Jacques, and D. L. 

Lorenz, Techniques for Estimating the Magnitude and Frequency of Floods of Ungauged 

Streams in Minnesota, Report 87-4170 (Washington, D.C.: U.S. Geological Survey, 1988); 

Vining, K.C., Simulation of Streamflow and Wetland Storage, Starkweather Coulee Subbasin, 

North Dakota, Water Years 1981-98, Water-Resources Investigations Report 02-4113 

(Bismarck, ND: U.S. Geological Survey, 2002), 33 p.; P. McEachern, et al., “Landscape Control 

of Water Chemistry in Northern Boreal Streams of Alberta,” Journal of Hydrology 323:303-324 

(2006); R.A. Gleason, et al. Estimating Water Storage Capacity of Existing and Potentially 

Restorable Wetland Depressions in a Subbasin of the Red River of the North, U.S. Geological 

Survey Open-File Report 2007-1159 (Reston, VA: U.S. Geological Survey, 2007), 36 p.). In 

some cases, however, where wetlands that serve as stream origins are already saturated prior to 

rainfall, they can convey stormwater quickly downstream and thus actually increase flood peaks. 

Id. at 227 (citing Bay, R., “Runoff from Small Peatland Watersheds,” Journal of Hydrology

9:90-102 (1969); A. Bullock, and M. Acreman, “The Role of Wetlands in the Hydrological 

Cycle,” Hydrology and Earth System Sciences 7:358-389 (2003)). This is because the wetland 

soil, if completely saturated, cannot store any additional water, making the wetland enable to 

store floodwater. 
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Wetlands that serve as stream origins have important chemical connections to 

downstream waters that affect the integrity of those waters. These wetlands contain diverse 

microbial populations that perform various chemical transformations, acting as source of 

compounds and influencing the water quality downstream. Id. at 5-28 (citing K.R. Reddy, and 

R.D. DeLaune, Biogeochemistry of Wetlands: Science and Applications, 774 p. (2008)). Sulfatereducing bacteria found in some headwater wetlands produce methylated mercury, which is then 

transported downstream by surface flows. Id. (citing O.K. Linqvist, et al., “Mercury in the 

Swedish Environment - Recent Research on Causes, Consequences, and Remedial Measures,”

Water Air and Soil Pollution 55:xi-xiii (1991); G. Mierle, and R. Ingram, “The Role of Humic 

Substances in the Mobilization of Mercury from Watersheds,” Water Air and Soil Pollution

56:349-357 (1991); C.T. Driscoll, et al., “The Role of Dissolved Organic Carbon in the 

Chemistry and Bioavailability of Mercury in Remote Adirondack Lakes,” Water Air and Soil 

Pollution 80:499-508 (1995); B.A. Branfireun, et al., “In situ Sulphate Stimulation of Mercury 

Methylation in a Boreal Peatland: Toward a Link Between Acid Rain and Methylmercury 

Contamination in Remote Environments,” Global Biogeochemical Cycles 13:743-750 (1999)). 

Wetlands, including those that serve as stream origins, are the principle sources of dissolved 

organic carbon (DOC) in forests to downstream waters. Id. (citing P.J. Mulholland, and E.J.

Kuenzler, “Organic Carbon Export from Upland and Forested Wetland Watersheds,” Limnology 

and Oceanography 24:960-966 (1979); N.R. Urban, et al., “Export of Dissolved Organic Carbon 

and Acidity from Peatlands,” Water Resources Research 25:1619-1628 (1989); B.W. Eckhardt 

and T.R. Moore, “Controls on Dissolved Organic Carbon Concentrations in Streams of Southern 

Quebec,” Canadian Journal of Fisheries and Aquatic Sciences 47:1537-1544 (1990); J.-F. 

Koprivnjak and T.R. Moore, “Sources, Sinks, and Fluxes of Dissolved Organic Carbon in 
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Subarctic Fen Catchments,” Arctic and Alpine Research 24:204-210 (1992); P. Kortelainen, 

“Content of Total Organic Carbon in Finnish Lakes and Its Relationship to Catchment 

Characteristics,” Canadian Journal of Fisheries and Aquatic Sciences 50:1477-1483 (1993); 

T.A. Clair, et al., “Exports of Carbon and Nitrogen from River Basins in Canada’s Atlantic 

Provinces,” Global Biogeochemical Cycles 8:441-450 (1994); D. Hope, et al., “A Review of the 

Export of Carbon in River Water: Fluxes and Processes,” Environmental Pollution 84:301-324

(1994); P.J. Dillon and L.A. Molot, “Effects of Landscape Form on Export of Dissolved Organic 

Carbon, Iron, and Phosphorus from Forested Stream Catchments,” Water Resources Research

33:2591-2600 (1997); S.E. Gergel, et al., “Dissolved Organic Carbon as an Indicator of the Scale 

of Watershed Influence on Lakes and Rivers,” Ecological Applications 9:1377-1390 (1999)). 

Export of DOC to downstream waters supports primary productivity, effects pH and buffering 

capacity, and regulates exposure to UV-B radiation. Id. at 5-29 (citing K.N. Eshelman and H.F. 

Hemond, “The Role of Organic Acids in the Acid-base Status of Surface Waters at Bickford 

Watershed, Massachusetts,” Water Resources Research 21:1503-1510 (1985); L.O. Hedin, et al., 

“Patterns of Nutrient Loss from Unpolluted Old-growth Temperate Forests: Evaluation of 

Biogeochemical Theory,” Ecology 76:493-509 (1995); D.W. Schindler and P.J. Curtis, “The 

Role of DOC in Protecting Freshwaters Subjected to Climate Warming and Acidification from 

UV Exposure,” Biogeochemistry 36:1-8 (1997); J.C. Nuff and G.P. Asner, “Dissolved Organic 

Carbon in Terrestrial Ecosystems: Synthesis and a Model,” Ecosystems 4:29-48 (2001)). 

Wetlands also act as sinks and transformers for pollutants, including excess nutrients, 

through such processes as denitrification, ammonia volatilization, microbial and plant biomass 

assimilation, sedimentation, sorption and precipitation, biological uptake, and long-term storage 

of plant detritus. Id. (citing K.C. Ewel and H.T. Odum, Cypress Swamps (Gainesville, FL: 
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University Presses of Florida, 1984); S.J. Nixon and V.J. Lee, Wetlands and Water Quality: A 

Regional Review of Recent Research in the United States on the Role of Freshwater and 

Saltwater Wetlands as Sources, Sinks, and Transformers of Nitrogen, Phosphorus, and Various 

Heavy Metals, Technical Report Y-86-2 (Vicksburg, MS: U.S. Army Corp of Engineers, 

Waterways Experiment Station, 1986); C. Johnston, “Sediment and Nutrient Retention by 

Freshwater Wetlands: Effects on Surface Water Quality,” Critical Reviews in Environmental 

Control 21:491-565 (1991); K.R. Reddy, et al., “Phosphorus Retention in Streams and Wetlands: 

A Review,” Critical Reviews in Environmental Science and Technology 29:83-146 (1999); W.J. 

Mitsch and J.G. Gosselink, Wetlands, 4th edition (Hoboken, NJ: John Wiley & Sons Inc., 2007); 

K.R. Reddy, and R.D. DeLaune, Biogeochemistry of Wetlands: Science and Applications (Boca 

Raton, FL: CRC Press, 2008); R.H. Kadlec and S.D. Wallace, Treatment Wetlands, 2nd edition

(Boca Raton, FL: CRC Press, 2009)). Specifically, wetlands reduce phosphorus, nitrate, and 

ammonium by large percentages. Id. at 5-30 (citing F.E. Dierberg and P.L. Brezonik, “Nitrogen 

and Phosphorus Mass Balances in a Cypress Dome Receiving Wastewater,” in K.C. Ewel and 

H.T. Odum, ed., Cypress Swamps (Gainesville, FL: University Presses of Florida, 1984), pp.

112-118; E.J. Dunne, et al., “Phosphorus Release and Retention by Soils of Natural Isolated 

Wetlands,” International Journal of Environment and Pollution 28:496-516 (2006); T.E. Jordan,

et al., “Comparing Functional Assessments of Wetlands to Measurements of Soil Characteristics 

and Nitrogen Processing,” Wetlands 27:479-497 (2007)). These processes are important for 

protecting downstream waters from pollutants from agricultural runoff. Wetland microbial 

processes reduce other pollutants, such as pesticides, hydrocarbons, heavy metals, and 

chlorinated solvents. Id. (citing R.R. Brooks, et al., “Cobalt and Nickel Uptake by the 

Nyssaceae,” Taxon 26:197-201 (1977); C.M. Kao, et al., “Non-point Source Pesticide Removal 
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by a Mountainous Wetland,” Water Science and Technology 46:199-206 (2002); P.I. Boon, 

“Biogeochemistry and Bacterial Ecology of Hydrologically Dynamic Wetlands,” in D. P. Batzer 

and R. R. Sharitz, ed., Ecology of Freshwater and Estuarine Wetlands (Berkeley, CA: University 

of California Press, 2006), pp. 115-176).

Tributary wetlands have important biological connections downstream that impact the 

integrity of (a)(1) through (a)(3) waters. Emergent and aquatic vegetation found in wetlands 

disperse by water, wind, and hitchhiking on migratory animals from tributary wetlands

downstream. Id. at 5-31 (citing M.B. Soons and G.W. Heil, “Reduced Colonization Capacity in 

Fragmented Populations of Wind-Dispersed Grassland Forbs,” Journal of Ecology 90:1033-1043

(2002); M.B. Soons, “Wind Dispersal in Freshwater Wetlands: Knowledge for Conservation and 

Restoration,” Applied Vegetation Science 9:271-278 (2006); C. Nilsson, et al., “The Role of 

Hydrochory in Structuring Riparian and Wetland Vegetation,” Biological Reviews 85:837-858

(2010)). Similarly, fish move between the river network and wetlands during times of surface 

water connections, and tributary wetlands by definition are connected on the surface to 

downstream waters. Id. at 5-32 (citing J.W. Snodgrass, et al., “Factors affecting the occurrence 

and structure of fish assemblages in isolated wetlands of the upper coastal plain, USA,”

Canadian Journal of Fisheries and Aquatic Sciences 53:443-454 (1996); K.D. Zimmer, et al., 

“Effects of fathead minnow colonization and removal on a prairie wetland ecosystem,”

Ecosystems 4:346-357 (2001); M.J. Baber, et al., “Controls on fish distribution and abundance in 

temporary wetlands,” Canadian Journal of Fisheries and Aquatic Sciences 59:1441-1450

(2002); M.A. Hanson, et al., “Biotic interactions as determinants of ecosystem structure in 

prairie wetlands: An example using fish,” Wetlands 25:764-775 (2005);, B.R. Herwig, et al., 

“Factors influencing fish distributions in shallow lakes in prairie and prairie-parkland regions of 
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Minnesota, USA,” Wetlands 30:609-619 (2010)). Mammals that can disperse overland can also 

contribute to connectivity. Id. (citing C.E. Shanks and G.C. Arthur, “Muskrat movements and 

population dynamics in Missouri farm ponds and streams,” Journal of Wildlife Management

16:138-148 (1952); W.R. Clark, “Ecology of muskrats in prairie wetlands,” in H.R. Murkin, et 

al., ed., Prairie Wetland Ecology: The Contribution of the Marsh Ecology Research Program,

(Ames, IA: Iowa State University Press, 2000), pp. 287-313). Insects also hitchhike on birds and 

mammals from tributary wetlands to the stream network, which can then serve as a food source 

for downstream waters. Id. (citing J. Figuerola and A.J. Green, “Dispersal of Aquatic Organisms 

by Waterbirds: A Review of Past Research and Priorities for Future Studies,” Freshwater 

Biology 47:483-494 (2002); J. Figuerola, et al., “Invertebrate Eggs Can Fly: Evidence of 

Waterfowl-Mediated Gene Flow in Aquatic Invertebrates,” American Naturalist 165:274-280 

(2005)). Insects that are flight-capable also use both stream and tributary wetlands, moving from 

the stream to the wetland to find suitable habitat for overwintering, refuge from adverse 

conditions, hunting, foraging, or breeding. Id. at 5-33 (citing D.D. Williams, “Environmental 

Constraints in Temporary Fresh Waters and Their Consequences for the Insect Fauna,” Journal 

of the North American Benthological Society 15:634-650 (1996); A.J. Bohonak and D.G. 

Jenkins, “Ecological and Evolutionary Significance of Dispersal by Freshwater Invertebrates,”

Ecology Letters 6:783-796 (2003)). Amphibians and reptiles, including frogs, toads, and newts,

also move between streams or rivers and tributary wetlands to satisfy part of their life history 

requirements, feed on aquatic insects, and avoid predators. Id. (citing V.S. Lamoureux and D.M. 

Madison, “Overwintering Habitats of Radio-Implanted Green Frogs, Rana clamitans,” Journal 

of Herpetology 33:430-435 (1999); K.J. Babbitt, et al., “Patterns of Larval Amphibian 

Distribution Along a Wetland Hydroperiod Gradient,” Canadian Journal of Zoology-Revue 
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Canadienne De Zoologie 81:1539-1552 (2003); S.B. Adams, et al., “Instream Movements by 

Boreal Toads (Bufo boreas boreas),” Herpetological Review 36:27–33 (2005); D.M. Green, 

“Bufo americanus, American Toad,” in M. Lannoo, ed., Amphibian Declines: The Conservation 

Status of United States Species (Berkeley, CA: University of California Press, 2005) , pp. 692-

704; T.W. Hunsinger and M.J. Lannoo, “Notophthalmus viridescens, Eastern Newt,” in M. 

Lannoo, ed., Amphibian Declines: The Conservation Status of United States Species (Berkeley, 

CA: University of California Press, 2005), pp. 912-914; J.W. Petranka and C.T. Holbrook, 

“Wetland Restoration for Amphibians: Should Local Sites Be Designed to Support 

Metapopulations or Patchy Populations?,” Restoration Ecology 14:404-411 (2006); A.L. 

Subalusky, et al., “Ontogenetic Niche Shifts in the American Alligator Establish Functional 

Connectivity between Aquatic Systems,” Biological Conservation 142:1507-1514 (2009)).

Lake, pond, and wetland tributaries, including wetlands that serve as stream origins, have 

important chemical, physical, and biological connections downstream that affect (a)(1) through 

(a)(3) waters and rivers. Their direct hydrologic connection to the stream network facilitates the 

significant impact they have downstream. This impact on downstream waters occurs regardless 

of whether their flow is perennial, intermittent, or ephemeral. Thus, lake, pond, and wetland 

tributaries serve the same important functions as stream tributaries, which in turn greatly impact 

downstream (a)(1) through (a)(3) waters, particularly when their functional contributions to the 

chemical, physical, and biological conditions of downstream waters are combined at a watershed 

scale.

H. Man-made or Man-altered Tributaries Significantly Affect the Physical, Chemical 

and Biological Integrity of (a)(1) through (a)(3) Waters
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The agencies’ proposed rule clarifies that man-made and man-altered tributaries as 

defined in the proposed rule are waters of the United States because the significant nexus 

between a tributary and a traditional navigable water or interstate water is not broken where the 

tributary flows through a culvert or other structure. The scientific literature indicates that 

structures that convey water do not affect the connectivity between streams and downstream 

rivers. Indeed, because such structures can reduce water losses from evapotranspiration and 

seepage, such structures likely enhance the extent of connectivity by more completely conveying 

the water downstream. 

Man-made and man-altered tributaries include impoundments, ditches, canals, 

channelized streams, piped, and the like. Ditches and canals are wide-spread across the United 

States. Ditches may have been streams that were channelized. They are purposely constructed to 

allow the hydrologic flow of the tributary to continue downstream. Man-made and man-altered 

tributaries, despite human manipulation, usually continue to have chemical, physical, and 

biological connections downstream and to serve important functions downstream. Because these 

tributaries are hydrologically connected to downstream waters, the chemical and some biological 

connections to downstream waters that are supported by this hydrologic connection are still 

intact. Often-times man-made tributaries create connections where they did not previously exist, 

such as canals that connect two rivers in different watersheds. 

Tributary ditches and other man-made or man-altered waters that meet the definition of 

“tributary” have a significant nexus to (a)(1) through (a)(3) waters due to their impact, either 

individually or with other tributaries, on the chemical, physical, or biological integrity of those 

downstream waters. Tributary ditches and the like, as with other tributaries, have physical, 

chemical, and biological connections with downstream waters that substantially impact those 
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waters. Tributary ditches and canals can have perennial, intermittent, or ephemeral flow. As 

described above, tributaries of all flow regimes have a significant nexus to downstream (a)(1) 

through (a)(3) waters. Due to the often straightened and channelized nature of ditches, these 

tributaries quickly move water downstream to (a)(1) through (a)(3) waters. Ditches and canals, 

like other tributaries, export sediment, nutrients, and other materials downstream. Due to their 

often channelized nature, ditches are very effective at transporting water and these materials, 

including nitrogen, downstream. See, e.g., J.P. Schmidt, et al., “Nitrogen Export from Coastal 

Plain Field Ditches,” Journal of Soil and Water Conservation 62(4):235-243; J.S. Strock, et al., 

“Managing Natural Processes in Drainage Ditches for Nonpoint Source Nitrogen Control.” 

Journal of Soil and Water Conservation 62(4): 188-196 (2007). Ditches provide habitat for fish 

and other aquatic organisms. See, e.g., P.C. Smiley, Jr., et al., “Contribution of Habitat and 

Water Quality to the Integrity of Fish Communities in Agricultural Drainage Ditches,” Journal 

of Soil and Water Conservation 63(6):218A-219A (2008). Fish and other aquatic organisms 

utilize canals and ditches to move to different habitats, sometimes over long distances. F.J. 

Rahel, “Biogeographic Barriers, Connectivity and Homogenization of Freshwater Faunas: It’s a 

Small World after All,” Freshwater Biology 52(4): 696-710 (2007).

These significant connections and functions continue even where the tributary has a 

natural or man-made break in its channel, bed and bank, or OHWM. The presence of a channel, 

bed and bank, and OHWM upstream or downstream of the break is an indication that 

connections still exist. The significant nexus between a tributary and a downstream water is not 

broken where the tributary flows underground for a portion of its length, such as in karst 

topography. The hydrologic connection still exists, meaning that the chemical and biological 

connections that are mediated by the hydrologic connection also still exist. Similarly, flow 
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through boulder fields does not sever the hydrologic connection. When a tributary flows through 

a wetland enroute to another or the same tributary, the significant nexus still exists even though 

the bed and bank or ordinary high watermark is broken for the length of the wetland. As 

discussed in Part II, section 1.G. of this appendix, in-stream wetlands provide numerous benefits 

downstream, and the presence of the wetland in stream can provide additional water quality

benefits to the receiving waters. Flow in flat areas with very low gradients may temporarily 

break the tributary’s bed and bank or OHWM, but these systems continue to have a significant 

nexus downstream. These are just illustrative examples of break in ordinary high watermark; 

there are several other types, all of which do not break the significant nexus between a tributary 

and the downstream (a)(1) to (a)(3) water. 

There are more than 80,000 dams in the United States, with over 6,000 exceeding 15 

meters in height. Report at 3-48 (citing U.S. Army Corps of Engineers, National Inventory of 

Dams (2009)). The purpose of a dam is to impound (store) water for any of several reasons (e.g.

flood control, human water supply, irrigation, livestock water supply, energy generation, 

containment of mine tailings, recreation or pollution control). See 

http://www.damsafety.org/layout/subsection.aspx?groupid=14&contentid=47. Many dams 

fulfill a combination of the above functions. Because the purpose of a dam is to retain water 

effectively and safely, the water retention ability of a dam is of prime importance. Water may 

pass from the reservoir to the downstream side of a dam by: passing through the main spillway 

or outlet works; passing over an auxiliary spillway; overtopping the dam; seepage through the 

abutments; and seepage under the dam. Id. All water retention structures are subject to seepage 

through their foundations and abutments. Department of the Army, U.S. Army Corps of 

Engineers, Engineering and Design – Design, Construction and Maintenance of Relief Wells, 
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EM 1110-2-1914 (Washington, D.C.: Department of the Army, 1992), p. 1-1. Thus waters 

behind a dam still maintain a hydrologic connection to downstream waters.

Numerous studies have shown that dams impede biotic movements, reducing biological 

connectivity between upstream and downstream locations. Report at 3-48 (citing E.A. 

Greathouse, et al., “Indirect Upstream Effects Of Dams: Consequences Of Migratory Consumer 

Extirpation In Puerto Rico,” Ecological Applications 16: 339-352 (2006); C.J. Hall, et al., “The 

Historic Influence of Dams on Diadromous Fish Habitat with a Focus on River Herring and 

Hydrologic Longitudinal Connectivity,” Landscape Ecology 26: 95-107(2011)). Dams alter but 

typically do not sever the hydrologic connection between upstream and downstream waters. (See 

Part II, section 2.C. of this appendix ). Upstream of large dams riparian areas are permanently 

inundated, increasing hydrological connectivity. Downstream, peak flows and the potential for 

overbank lateral flow are reduced; however, dams may also reduce flow variability downstream, 

resulting in higher minimum flows and reduced flow intermittency and thereby increasing 

hydrological (and potentially biological) connectivity. Id. (citing N.L. Poff, et al., 

“Homogenization of Regional River Dynamics by Dams and Global Biodiversity Implications,” 

Proceedings of the National Academy of Sciences of the United States of America 104: 5732-

5737 (2007)). Where an impoundment does stop flow, it also has significant effects on 

downstream waters. For example, the downstream segments have a reduced quantity of waters, 

less sediment, and reduced species biological connectivity with upstream refugia.

Because dams reduce the amount of sediment delivered downstream, the reservoirs 

behind dams are actually very effective at retaining sediment, which can have significant effects 

in downstream waters. For instance, the Mississippi River’s natural sediment load has been 

reduced by an estimated 50% through dam construction in the Mississippi Basin. M.D. Blum, 
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and H. H. Roberts, “Drowning of the Mississippi Delta Due to Insufficient Sediment Supply and 

Global Sea-Level Rise,” Nature Geoscience 2(7): 488-491 (2009).

Man-made or man-altered tributaries continue to have physical, chemical and biological 

connections that significantly affect the integrity of (a)(1) through (a)(3) waters. Though the 

man-made or man-altered nature of such tributaries can change the nature of the connections, it 

does not eliminate them. Thus, man-made and man-altered tributaries continue to serve the same 

important functions as “natural” tributaries, which in turn greatly impact downstream (a)(1) 

through (a)(3) waters, particularly when their functional contributions to the chemical, physical, 

and biological conditions of downstream waters are combined at a watershed scale.

ii. Adjacent Waters

Adjacent waters, including adjacent wetlands, alone or in combination with other 

adjacent waters in the watershed, have a substantial impact on the chemical, physical, and 

biological integrity of traditional navigable waters, interstate waters, and the territorial seas. In 

addition, waters adjacent to tributaries serve many important functions that directly influence the 

integrity of downstream waters including traditional navigable waters, interstate waters, and the 

territorial seas. Adjacent waters store water, which can reduce flooding of downstream waters,

and the loss of adjacent waters has been shown, in some circumstances, to increase downstream 

flooding. Adjacent waters maintain water quality and quantity, trap sediments, store and modify 

potential pollutants, and provide habitat for plants and animals, thereby sustaining the biological 

productivity of downstream rivers, lakes and estuaries, which may be traditional navigable 

waters, interstate waters, or the territorial seas. The scientific literature and Report supports these 

conclusions, as discussed in greater detail below.
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1. Adjacent waters under this proposed rule have a significant nexus to (a)(1) through 

(a)(3) waters.

The discussion below summarizes the key points made in the Report and explains the 

technical basis for supporting a conclusion that adjacent waters, as defined in this proposed rule, 

have a significant nexus to waters identified in paragraphs (a)(1) – (a)(3) of the proposed rule. 

The geographic position of an “adjacent” water relative to the stream is indicative of the 

relationship they share, with many of its defining characteristics resulting from the movement of 

materials and energy between the two. A review and analysis of the scientific literature supports 

the conclusion that individually or in combination with similarly situated waters in a watershed, 

adjacent waters have a significant effect on the chemical, physical, and biological integrity of 

downstream traditionally navigable waters, interstate waters, and territorial seas.

a. Riparian and Floodplain Waters Significantly Affect the Chemical, Physical, and 

Biological Integrity of (a)(1) through (a)(3) Waters

Waters, including wetlands, often lie within landscape settings that have bidirectional 

hydrological exchange with (a)(1) through (a)(5) waters (e.g., wetlands and open waters in 

riparian areas and flood plains). Such waters play an integral role in the chemical, physical, and 

biological integrity of the waters to which they are adjacent. Riparian areas and floodplains often 

describe the same geographic region. Report at 3-4. Therefore, the discussion of the functions of 

waters, including wetlands, in riparian areas will typically apply to floodplains unless otherwise 

noted. Where connections arise specifically from the act of inundation of adjacent land during 

times of higher-than-normal water, the term “floodplain” is solely used to describe the area.

Riparian areas are transition zones between terrestrial and aquatic ecosystems that are 

distinguished by gradients in biophysical conditions, ecological processes, and biota. Id., Report
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at 31. Waters including wetlands in riparian areas significantly influence exchanges of energy 

and matter with aquatic ecosystems. See, e.g., id. (citing National Research Council, Riparian 

Areas: Functions and Strategies for Management (Washington, D.C.: The National Academies 

Press, 2002).

Floodplains are low gradient areas bordering stream or river channels, lakes, and 

impoundments that were formed by sediment deposition from those waters under present 

climatic conditions. These natural geomorphic features are inundated during moderate to high 

water events. Id. (citing L.B. Leopold, A View of the River (Cambridge, MA: Harvard University 

Press, 1994); W.R. Osterkamp, Annotated Definitions of Selected Geomorphic Terms and 

Related Terms of Hydrology, Sedimentology, Soil Science and Ecology, USGS Open File Report 

2008-1217 (Reston, VA: U.S. Department of the Interior, U.S. Geological Survey, 2008)). By 

“present climactic conditions,” the agencies mean that currently or recently active floodplains 

will be used to help determine whether wetlands or waters are adjacent to waters of the United 

States. The proposed definition is limited to the present climactic conditions in order to best 

represent the floodplain that has an active and significant relationship with the stream or river 

channel. Historic floodplains that played a role in the river or lake dynamics in the past only will 

not be used to determine whether a water is adjacent. Floodplains formed under different 

climactic conditions that no longer connect to the stream channel that formed them are terraces.

Id. It should be noted that “floodplain” as defined in today’s proposed rule does not necessarily 

equate to the 100-year floodplain as defined by the Federal Emergency Management Agency 

(FEMA). However, the FEMA defined floodplain may often coincide with the current definition 

proposed in this rule. Flood insurance rate maps are based on the probability of a flood event 

occurring (e.g., 100-year floods have a 1% probability of occurring in a given year or 500 year-
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floods have a 0.2% probability of occurring in a particular year). Flood insurance rate maps are 

not based on an ecological definition of the term “floodplain,” and therefore do not have any use 

in identifying adjacent wetlands and waters for the purposes of CWA jurisdiction. Flood 

insurance rate maps are developed by applying models and other information to identify areas 

that would be inundated by a flood event of a particular probability of recurring. 

Riparian waters take many different forms. Some may be wetlands, which are defined in 

paragraph (c)(6) of the proposed rule. Others may be ponds, oxbow lakes, or other types of open 

waters. Oxbow lakes, commonly found in floodplains, are formed when river meanders are 

cutoff from the rest of the river. Id. at 5-42. 

b. Riparian and Floodplain Waters Significantly Affect the Physical Integrity of 

(a)(1) through (a)(3) Waters

Scientific research shows waters and wetlands in riparian areas and floodplains to be 

important in protecting the physical integrity of aquatic resources. Because riparian and 

floodplain waters exhibit bidirectional exchange of water with the waters to which they are 

adjacent, they play an important role in determining the volume and duration of stream flow. 

Riparian and floodplain waters also have an essential role in regulating and stabilizing sediment 

transport to downstream waters. These characteristics are fundamental to the physical integrity of 

streams as well as downstream traditional navigable waters, interstate waters, and territorial seas. 

Riparian and floodplain wetlands are important for the reduction or delay of floods. Id.at

3-22 (citing A. Bullock and M. Acreman, “The Role of Wetlands in the Hydrological Cycle,” 

Hydrology and Earth System Sciences 7:358-389 (2003)). Waters in riparian areas control 

flooding during times of high precipitation or snowmelt by capturing water from overbank flow 

and storing excess stream water. Id. at 5-6. One study found that peak flows in the Cache River 
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in Arkansas decreased by 10-20% mainly because of floodplain water storage. Id. (citing R. 

Walton, et al., “Hydrology of the Black Swamp Wetlands on the Cache River, Arkansas,”

Wetlands 16:279-287 (1996). Research has shown that floodplain wetlands in Ohio store about 

40% of the flow of small streams. Id. at 5-6 to 5-7 (citing D.E. Gamble, et al., An Ecological and 

Functional Assessment of Urban Wetlands in Central Ohio. Columbus, Ohio, EPA Technical 

Report WET/ 2007-3B, (Columbus, OH: Ohio Environmental Protection Agency, Wetland 

Ecology Group, Division of Surface Water, 2007)). These and similar findings point to the close 

hydrological influence that waters in riparian and floodplain areas have on streams. 

Some adjacent waters are bordering or contiguous with (a)(1) through (a)(5) waters. 

Because of their close physical proximity to nearby waterbodies, they readily exchange their 

waters through the saturated soils surrounding the stream or through surface exchange. This 

commingling of waters allows bordering or contiguous waters to both provide chemically 

transformed waters to streams and to absorb excess stream flow. 

Flow between neighboring waters and streams is more longitudinal (downslope) at 

headwaters and more lateral further downstream. Id. at 5-38, Table 5-3. These connections in 

part determine stream flow volume and duration. Waters, including wetlands, in riparian areas 

connect to neighboring waterbodies through various surface and subsurface connections. See, 

e.g., id. at 3-4 (citing National Research Council, Riparian Areas: Functions and Strategies for 

Management (Washington, D.C.: National Academy Press, 2002)). Floodplains, similarly, are 

closely associated with the groundwater found beneath and beside river channels (which are 

considered shallow aquifers) and waters in floodplains readily exchange water with such 

aquifers. Id. at 3-14 (citing J.A. Stanford and J. V. Ward, “An Ecosystem Perspective of Alluvial 

Rivers: Connectivity and the Hyporheic Corridor,” Journal of the North American Benthological 
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Society 12:48-60 (1993); C. Amoros and G. Bornette, “Connectivity and Biocompexity in 

Waterbodies of Riverine Floodplains,” Freshwater Biology 47:761-776 (2002); G.C. Poole, et 

al., “Multiscale Geomorphic Drivers of Groundwater Flow Paths: Subsurface Hydrologic 

Dynamics and Hyporheic Diversity,” Journal of the North American Benthological Society

25:288-303 (2006)). Riparian and floodplain wetlands are frequently contiguous with streams 

and other waterbodies and significantly influence the hydrology of such waterbodies. Id. at 5-6

(citing R.J. Naiman, et al., Riparia: Ecology, Conservation, and Management of Streamside 

Communities (Burlington, MA: Elsevier Academic Press, 2005); P. Vidon, et al., “Hot Spots and 

Hot Moments in Riparian Zones: Potential for Improved Water Quality Management,” Journal 

of the American Water Resources Association 46:278-298 (2010)). Floodplain wetlands are 

important for the reduction or delay of floods. Id. (citing A. Bullock and M. Acreman, “The Role 

of Wetlands in the Hydrological Cycle,” Hydrology and Earth System Sciences 7:358-389

(2003)). Oxbow lakes also retain flood waters. Id. at 5-44. Adjacent ponds generally function 

similarly to oxbow lakes. 

Waters in riparian areas filter sediment washed down from uplands and collect sediment 

from overbank flow as the river or stream floods. Id. at 5-7. For example, riparian areas were 

observed to collect 80-90% of the sediment from farmlands in a study in North Carolina. Id.

(citing A. Cooper, et al., “Riparian Areas as Filters for Agricultural Sediment,” Soil Science 

Society of America Proceedings 51:416-420 (1987); R.B. Daniels and J.G. Gilliam, “Sediment 

and Chemical Load Reduction by Grass and Riparian Filters,” Soil Science Society of America 

Journal 60:246-251 (1996); R.J. Naiman and H. Decamps, “The Ecology of Interfaces: Riparian 

Zones,” Annual Review of Ecology and Systematics 28:621-658 (1997)). Maintaining the 

equilibrium between sediment deposition and sediment transport is important to maintain the 
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physical shape and structure of stream channels. Significant changes to upstream channels can 

affect the chemical, physical, and biological condition of downstream (a)(1) through (a)(3) 

waters. 

The physical effects of excess sediment can impair chemical and ecological integrity in a 

variety of ways. Id. at 5-9 (citing P.J. Wood and P.D. Armitage, “Biological Effects of Fine 

Sediment in the Lotic Environment,” Environmental Management 21:203-217 (1997)). Excess 

sediment is linked to increasing contaminant and nutrient concentrations, all of which tributaries 

can transmit downstream, affecting water quality. Excess sediment may block and absorb 

sunlight transmission through the water column, inhibiting plant photosynthesis and warming the 

water in the stream. Sediment may fill the interstitial spaces between rocks in a streambed, which 

many fish and aquatic species use for mating, reproduction, and shelter from predators. This kind 

of physical degradation of tributary streambeds results in less suitable habitat available for 

animals and fish that move between upstream and downstream waters. Riparian waters that 

retain sediments thus protect downstream waters from the effects of excess sediment. 

Oxbow lakes play similar roles in the floodplain as they are an integral part of alluvial 

floodplains of meandering rivers. Id. at 5-42 (citing K.O. Winemiller, et al., “Fish Assemblage 

Structure in Relation to Environmental Variation among Brazos River Oxbow Lakes,”

Transactions of the American Fisheries Society 129:451-468 (2000), K. Glinska-Lewczuk, 

“Water Quality Dynamics of Oxbow Lakes in Young Glacial Landscape of NE Poland in 

Relation to Their Hydrological Connectivity,” Ecological Engineering 35:25-37 (2009)). They 

connect to rivers by periodic overland flow, typically from the river during flooding events, and 

bidirectional shallow subsurface flow through fine river soils (bidirectional means flow from 

river to lake and lake to river). Id. at 5-43 to 5-44. Oxbow lakes generally have an important
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influence on the condition and function of rivers. Id. at 5-48 to 5-49. That influence can vary 

with the distance from the river and the age of the oxbow, reflecting the frequency and nature of 

the exchange of materials that takes place between the two waterbodies. 

Because adjacent waters support riparian vegetation, they affect the capacity of riparian 

vegetation to influence stream flow, morphology, and habitat provided in the nearby waterbody. 

Vegetation in riparian waters influences the amount of water in the stream by capturing and 

transpiring stream flow and intercepting groundwater and overland flow. Id. at 3-22, 5-7 (citing 

P. Meyboom, “Three Observations on Streamflow Depletion by Phreatophytes,” Journal of 

Hydrology 2:248-261 (1964)). Riparian vegetation in adjacent waters also reduces stream bank 

erosion, serving to maintain the physical integrity of the channel. See, e.g., id. at 5-8 (citing C.E. 

Beeson and P. F. Doyle, “Comparison of Bank Erosion at Vegetated and Non-Vegetated Channel 

Bends,” Journal of the American Water Resources Association 31:983-990 (1995)). In addition, 

inputs of woody debris from aquatic vegetation into waters make important contributions to the 

channel’s geomorphology and the stream’s aquatic habitat value. Id. (citing N.H. Anderson and 

J. R. Sedell, “Detritus Processing by Macroinvertebrates in Stream Ecosystems,” Annual Review 

of Entomology 24:351-377 (1979); M.E. Harmon, et al., “Ecology of Coarse Woody Debris in 

Temperature Ecosystems,” Advances in Ecological Research 15:133-302 (1986); F. Nakamura 

and F. J. Swanson, “Effects of Coarse Woody Debris on Morphology and Sediment Storage of a 

Mountain Stream System in Western Oregon,” Earth Surface Processes and Landforms 18:43-61

(1993); T.E. Abbe and D. R. Montgomery, “Large Woody Debris Jams, Channel Hydraulics and 

Habitat Formation in Large Rivers,” Regulated Rivers: Research & Management 12:201-221

(1996); R.J. Naiman and H. Decamps, “The Ecology of Interfaces: Riparian Zones,” Annual 

Review of Ecology and Systematics 28:621-658 91997); A.M. Gurnell, et al., “Large Wood and 
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Fluvial Processes,” Freshwater Biology 47:601-619 (2002)). Also, the riparian vegetation that 

overhangs streams provides shade, providing a critically important function of reducing 

fluctuations in water temperature helping to reduce excessive algal production and to maintain 

life-supporting oxygen levels in streams and other waters. Id. at 5-9 (citing S.V. Gregory, et al., 

“An Ecosystem Perspective of Riparian Zones: Focus on Links between Land and Water,”

Bioscience 41:540-551 (1991); E.C. Volkmar and R.A. Dahlgren, “Biological Oxygen Demand 

Dynamics in the Lower San Joaquin River, California,” Environmental Science & Technology

40:5653-5660 (2006)). Even small changes in water temperature can have significant impacts on 

the type and number of species present in waters, with higher temperatures generally associated 

with degraded habitat which supports only those species that can tolerate higher temperatures 

and reduced levels of dissolved oxygen. Higher water temperatures are associated with streams 

and rivers with less valuable recreational and commercial fisheries. As discussed below, these 

physical characteristics of headwater streams influence what types of organisms live in the 

region. 

Headwaters and nearby wetlands supply downstream waters with dissolved organic 

carbon as a result of decomposition processes from dead organic matter such as plants. The 

biological consequences of this dissolved organic carbon are discussed in more detail below. The 

presence of dissolved organic carbon can affect how light penetrates the water, an important 

factor in the growth of plants, algae, and other primary producers, and can protect aquatic 

organisms from the harmful effects of UV-B radiation. Id. at 5-28 to 5-29 (citing K.N. Eshelman 

and H.F. Hemond, “The role of organic acids in the acid-base status of surface waters at 

Bickford Watershed, Massachusetts,” Water Resources Research 21:1503-1510 (1985); J.E. 

Hobbie and R.G. Wetzel, “Microbial control of dissolved organic carbon in lakes: Research for 
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the future,” Hydrobiologia 229:169-180 (1992); D.W. Schindler and P.J. Curtis, “The role of 

DOC in protecting freshwaters subjected to climate warming and acidification from UV 

exposure,” Biogeochemistry 36:1-8 (1997); K.R. Reddy and R.D. DeLaune, Biogeochemistry of 

Wetlands: Science and Applications, (Boca Raton, FL: CRC Press, 2008)). 

c. Riparian and Floodplain Waters Significantly Affect the Chemical Integrity of 

(a)(1) through (a)(3) Waters

As stated above in the section on tributaries, pollutants such as petroleum waste products 

and other harmful pollutants dumped into any part of the tributary system are likely to flow 

downstream, or to be washed downstream, and thereby pollute navigable or interstate waters, 

from which American citizens take their drinking water, shellfish, fin fish, water-based 

recreation, and many other uses. Some wetlands perform the valuable function of trapping or 

filtering out some pollutants (such as fertilizers, silt, and some pesticides), thereby reducing the 

likelihood that those pollutants will reach and pollute the tributaries of the downstream navigable 

or interstate waters (and eventually pollute those downstream waters themselves). However, 

many other pollutants (such as petroleum wastes and toxic chemical wastes), if dumped into 

wetlands or other waters that are adjacent to tributary streams, may reach those tributaries 

themselves, and thereafter flow downstream to pollute the nation’s drinking water supply, 

fisheries, and recreation areas.

Riparian and floodplain waters play a critical role in controlling the chemicals that enter 

streams and other waters of the United States and as a result are vital in protecting the chemical,

physical, and biological integrity of downstream (a)(1) through (a)(3) waters. Runoff (the water 

that has not evaporated or infiltrated into the groundwater) from uplands is a large source of 

pollution, but research has shown that wetlands and other riparian waters trap and chemically 
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transform a substantial amount of the nutrients, pesticides, and other pollutants before they enter 

streams, river, lakes and other waters.

Chemicals and other pollutants enter waters from point sources, non-point sources, 

atmospheric deposition, upstream reaches, and through the hyporheic zone, a region beneath and 

alongside a stream bed where surface water and shallow groundwater mix. Id. at 5-10 (citing 

S.W. Nixon and V.J. Lee, Wetlands and Water Quality: A Regional Review of Recent Research 

in the United States on the Role of Freshwater and Saltwater Wetlands as Sources, Sinks, and 

Transformers of Nitrogen, Phosphorus, and Various Heavy Metals, Technical Report Y-86-2, 

(Vicksburg, MS: U.S. Army Corp of Engineers, Waterways Experiment Station, 1986); D.F.

Whigham and T.E. Jordan, “Isolated Wetlands and Water Quality,” Wetlands 23:541-549

(2003); S.L.Whitmire and S.K. Hamilton, “Rates of Anaerobic Microbial Metabolism in 

Wetlands of Divergent Hydrology on a Glacial Landscape,” Wetlands 28:703-714 (2008)). 

Throughout the stream network, but especially in headwater streams and their adjacent wetlands, 

chemicals are sequestered, assimilated, transformed, or lost to the atmosphere by microbes, 

fungi, algae, and macrophytes present in riparian waters and soils. Id. (citing S.W. Nixon and 

V.J. Lee, Wetlands and Water Quality: A Regional Review of Recent Research in the United 

States on the Role of Freshwater and Saltwater Wetlands as Sources, Sinks, and Transformers of 

Nitrogen, Phosphorus, and Various Heavy Metals, Technical Report Y-86-2, (Vicksburg, MS: 

U.S. Army Corp of Engineers, Waterways Experiment Station, 1986); C. Johnston, “Sediment 

and Nutrient Retention by Freshwater Wetlands: Effects on Surface Water Quality,” Critical 

Reviews in Environmental Control 21:491-565 (1991); P.I. Boon, “Biogeochemistry and 

Bacterial Ecology of Hydrologically Dynamic Wetlands,” in D.P. Batzer and R.R. Sharitz, ed.,

Ecology of Freshwater and Estuarine Wetlands (Berkeley, CA: University of California Press, 
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2006), pp. 115-176; W.J. Mitsch and J.G. Gosselink, Wetlands, 4th edition, (Hoboken, NJ: John 

Wiley & Sons Inc., 2007); K.R., Reddy and R.D. DeLaune, Biogeochemistry of Wetlands: 

Science and Applications (Boca Raton, FL: CRC Press, 2008). These chemical processes reduce 

or eliminate pollution that would otherwise enter streams, rivers, lakes and other waters and 

subsequently downstream traditional navigable waters, interstate waters, or the territorial seas. 

The removal of the nutrients nitrogen and phosphorus is a particularly important role for riparian 

waters. Nutrients are necessary to support aquatic life, but the presence of excess nutrients can 

lead to eutrophication and the depletion of oxygen nearby waters and in waters far downstream. 

See, e.g., id. at 1-8. Eutrophication is a large problem in waters across the United States 

including such significant ecosystems as the Chesapeake Bay and Lake Spokane in Washington. 

W.M. Kemp, et al., “Eutrophication of Chesapeake Bay: Historical Trends and Ecological 

Interactions,” Marine Ecology Progress Series 303(21):1-29 (2005); D.J. Moore and J. Ross, 

Spokane River and Lake Spokane Dissolved Oxygen Total Maximum Daily Load: Water Quality 

Improvement Report, Publication No. 07-10-073 (Spokane, WA: Washington State Department 

of Ecology, 2010); R.R. Murphy, et al., “Long-Term Trends in Chesapeake Bay Seasonal 

Hypoxia, Stratification, and Nutrient Loading,” Estuaries and Coasts 34(6):1293-1309 (2011).

Eutrophication is the process by which plants and algae grow in waters to such an extent that the 

abundance of vegetation monopolizes the available oxygen, detrimentally affecting other aquatic 

organisms. Id. Oxbow lakes also have high mineralization rates, suggesting that similar to

adjacent wetlands they process and trap nutrients from runoff. Report at 5-45 to 5-46 (citing K.O. 

Winemiller, et al., “Fish Assemblage Structure in Relation to Environmental Variation among 

Brazos River Oxbow Lakes,” Transactions of the American Fisheries Society 129:451-468
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(2000)). Protection of these waters therefore helps maintain the chemical integrity of the nation’s 

waters. 

The removal of nitrogen is an important function of all waters, including wetlands, in the 

riparian areas. Riparian areas regularly remove more than half of dissolved nitrogen found in 

surface and subsurface water by plant uptake and microbial transformation. Id. at 5-11 (citing P. 

Vidon, et al., “Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water 

Quality Management,” Journal of the American Water Resources Association 46:278-298

(2010)). Denitrification in surface and subsurface flows is highest where there is high organic 

matter and/or anoxic conditions. Id. Denitrification occurs in wetland soils where there is high 

organic matter, low oxygen, denitrifying microbes, and saturated soil conditions, and rates 

increase with proximity to streams. Id. (citing S.V. Gregory, et al., “An Ecosystem Perspective 

of Riparian Zones: Focus on Links between Land and Water,” Bioscience 41:540-551 (1991); P. 

Vidon, et al., “Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water 

Quality Management,” Journal of the American Water Resources Association 46:278-298

(2010)). Riparian waters are therefore important in maintaining the conditions important for 

denitrification, which in turn protects streams, rivers, lakes and other waters from nitrogen 

pollution.

Plant uptake of dissolved nitrogen in subsurface flows also accounts for large quantities 

of nitrogen removal. Riparian forests have been found to remove 75% of dissolved nitrate 

transported from agricultural fields in Maryland. Id. (citing P. Vidon, et al., “Hot Spots and Hot 

Moments in Riparian Zones: Potential for Improved Water Quality Management,” Journal of the 

American Water Resources Association 46:278-298 (2010)). Likewise, riparian forests in 

Georgia remove 65% of nitrogen and 30% of phosphorus from agricultural sources. Id. at 5-11 to 
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5-12 (citing Vidon, et al. 2010). A Pennsylvania forest removed 26% of the nitrate from the 

subsurface. Id. at 5-12 (citing J.D. Newbold, et al., “Water Quality Functions of a 15-Year-Old 

Riparian Forest Buffer System,” Journal of the American Water Resources Association 46:299-

310 (2010)). The vegetation associated with riparian waters also removes nitrogen from 

subsurface flows. Therefore, the conservation of riparian waters helps protect downstream waters 

from influxes of dissolved nitrogen. 

Phosphorus is another potentially harmful nutrient that is captured and processed in 

riparian waters. Id. (citing T.A. Dillaha and S.P. Inamdar, “Buffer Zones as Sediment Traps or 

Sources,” in N.E. Haycock, T.P. Burt, K.W.T. Goulding, and G. Pinay, ed., Buffer Zones: Their 

Processess and Potential in Water Protection, Proceedings of the International Conference on 

Buffer Zones, September 1996 (Hertfordshire, UK: Quest Environmental, 1997), pp. 33-42; A.N.

Sharpley and S. Rekolainen, “Phosphorus in Agriculture and Its Environmental Implications,” in

H. Tunney, et al., ed., Phosphorus Losses from Soil to Water (Cambridge, UK: CAB 

International, 1997), pp. 1-54; G.C. Carlyle and A.R. Hill, “Groundwater Phosphate Dynamics in 

a River Riparian Zone: Effects of Hydrologic Flowpaths, Lithology, and Redox Chemistry,”

Journal of Hydrology 247:151-168 (2001)). Biogeochemical processes, sedimentation, and plant 

uptake account for high rates of removal of particulate phosphorus in riparian areas. Id. (citing 

C.C. Hoffmann, et al., “Phosphorus Retention in Riparian Buffers: Review of Their Efficiency,”

Journal of Environmental Quality 38:1942-1955 (2009)). The amount of contact the water has 

with nearby soils determines the ability of the riparian area to remove phosphorus. Id. This 

function of upstream riparian waters is crucial for maintaining the chemical and biological 

integrity of the waters to which they are adjacent, and for preventing eutrophication in 

downstream traditional navigable waters, interstate waters, and the territorial seas.
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d. Riparian and Floodplain Waters Significantly Affect the Biological Integrity of 

(a)(1) through (a)(3) Waters

Waters and wetlands located in both riparian areas and floodplains support the biological 

integrity of downstream (a)(1) through (a)(3) waters in a variety of ways. They provide habitat 

for aquatic and water-tolerant plants, invertebrates, and vertebrates, and provide feeding, refuge, 

and breeding areas for invertebrates and fish. Seeds, plants, and animals move between waters in 

the riparian zone and floodplains and the adjacent streams, and from there colonize or utilize 

downstream waters, including traditional navigable waters.

Organic matter from adjacent wetlands is critical to aquatic food webs, particularly in 

headwaters, where it is the primary source of energy flow due to low light conditions that inhibit 

photosynthesis. Id. at 5-13 (citing J.L. Tank, et al., “A Review of Allochthonous Organic Matter 

Dynamics and Metabolism in Streams,” Journal of the North American Benthological Society

29:118-146 (2010)). Headwater streams tend to be located in heavily vegetated areas compared 

to larger waters, so they are more likely to contain leaf litter, dead and decaying plants, and other 

organic matter that forms the basis of headwater food webs. The organic matter is processed by 

microbes and insects that make the energy available to higher levels of stream life such as 

amphibians and fish. Studies have shown that macroinvertebrates rely on leaf inputs in 

headwater streams and that excluding organic litter from a stream resulted in significant changes 

to the food web at multiple levels. Id. (citing G.W. Minshall, “Role of Allochthonous Detritus in 

the Tropic Structure of a Woodland Springbrook Community,” Ecology 48:139-149 (1967); J.B. 

Wallace, et al., “Multiple Trophic Levels of a Forest Stream Linked to Terrestrial Litter Inputs,”

Science 277:102-104 (1997); J.L. Meyer, et al., “Leaf Litter as a Source of Dissolved Organic 

Carbon in Streams,” Ecosystems 1:240-249 (1998)). Fish and amphibian species found in 
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headwaters travel downstream and in turn become part of the food web for larger aquatic 

organisms in rivers and other waters. Organic material provided by riparian waters to small, 

headwater streams is therefore important not only to the small streams that directly utilize this 

source of energy to support their biological populations but also to the overall biological integrity 

of downstream waters that also benefit from the movement of fish and other species that 

contribute to the food web of larger streams and rivers.

Floodplain water bodies, including oxbow lakes, accumulate organic carbon, an 

important function influenced by the size and frequency of floods from adjacent rivers. See, e.g., 

id. at 5-45 (citing A. Cabezas, et al., “Changing Patterns of Organic Carbon and Nitrogen 

Accretion on the Middle Ebro Floodplain (NE Spain),” Ecological Engineering 35:1547-1558

(2009)). These stored chemicals are available for exchange with river water when hydrological 

connections form. Organic materials are the basis for the food web in stream reaches where 

photosynthetic production of energy is absent or limited, particularly in headwater systems 

where vegetative litter alone makes up the base of the aquatic food web. The maintenance of 

floodplain waters is therefore an important component of protecting the biological integrity of 

downstream waters into which the headwaters flow. 

The waters, including wetlands, in the riparian area play an important role in the removal 

of pesticides. Id. at 5-14 (citing P. Vidon, et al., “Hot Spots and Hot Moments in Riparian Zones: 

Potential for Improved Water Quality Management,” Journal of the American Water Resources 

Association 46:278-298 (2010). Microbes near plant roots break down these pesticides. See, e.g.,

id. (citing G. Voos, and P.M. Groffman, “Relationships between microbial biomass and 

dissipation of 2,4-D and dicamba in soil,” Biology and Fertility of Soils 24:106-110 (1996)).

Uptake by aquatic plants has also been shown to be an important mechanism of removal of the 
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pesticides alachlor and atrazine. Id. (citing K.G. Paterson and J.L. Schnoor, “Fate of Alachlor 

and Atrazine in a Riparian Zone Field Site,” Water Environment Research 64:274-283 (1992)). 

Riparian waters also trap and hold pesticide contaminated runoff preventing it from harming 

neighboring waters.

Riparian areas are dynamic places that support a diversity of aquatic, amphibious, and 

terrestrial species adapted to the unique habitat created by periodic flooding events. Id. at 5-15

(citing W.J. Junk, et al., “The flood pulse concept in river-floodplain systems,” in D.P. Dodge, 

ed., Proceedings of the International Large River Symposium Ottawa (Ottawa, Canada: 

Canadian Special Publication of Fisheries and Aquatic Sciences 106, 1989), pp. 110-127; K. 

Tockner, et al., “An Extension of the Flood Pulse Concept,” Hydrological Processes 14:2861-

2883 (2000); C.T. Robinson, et al., “The Fauna of Dynamic Riverine Landscapes,” Freshwater 

Biology 47:661-677 (2002)). Plants, invertebrates, and vertebrates use waters, including 

wetlands, in the riparian areas for habitat, nutrients, and breeding. As a result, the waters, 

including wetlands, in the riparian areas act as sources of organisms, particularly during 

inundation events, replenishing neighboring waters with organisms, seeds, and organic matter. 

Inundation and hydrological connectivity of riparian areas greatly increase the area of aquatic 

habitats and species diversity. Id. at 5-15 to 5-16 (citing W.J. Junk et al. 1989; R. Jansson, et al., 

“Hydrochory Increases Riparian Plant Species Richness: A Comparison between a Free-Flowing 

and a Regulated River,” Journal of Ecology 93:1094-1103 (2005)). Aquatic animals, including 

amphibians and fish, take advantage of the waters present in riparian areas, either inhabiting 

them or moving between the riparian water and neighboring waters. Id. at 5-15, 5-17, 5-19 

(citing G.H. Copp, “The habitat diversity and fish reproductive function of floodplain 

ecosystems,” Environmental Biology of Fishes 26:1-27 (1989); L.A. Smock, et al., “Lotic 
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macroinvertebrate production in three dimensions: Channel surface, hyporheic, and floodplain 

environments,” Ecology 73:876-886 (1992); L.A. Smock, “Movements of invertebrates between 

stream channels and forested floodplains,” Journal of the North American Benthological Society

13:524-531 (1994); C. T. Robinson, et al., “The fauna of dynamic riverine landscapes,”

Freshwater Biology 47:661-677 (2002); J.S. Richardson, et al., “Riparian communities 

associated with Pacific Northwest headwater streams: Assemblages, processes, and uniqueness,” 

Journal of the American Water Resources Association 41:935-947 (2005); C. Ilg, et al., “Longterm reactions of plants and macroinvertebrates to extreme floods in floodplain grasslands,”

Ecology 89:2392-2398 (2008); D.E. Shoup, and D. H. Wahl, “Fish diversity and abundance in 

relation to interannual and lakespecific variation in abiotic characteristics of floodplain lakes of 

the lower Kaskaskia River, Illinois,” Transactions of the American Fisheries Society 138:1076-

1092 (2009)). Likewise, seeds, plant fragments, and whole plants move between riparian and 

floodplain waters and the river network. Id. at 5-15 (citing R.L. Schneider, and R.R. Sharitz, 

“Hydrochory and regeneration in a bald cypress water tupelo swamp forest,” Ecology 69:1055-

1063 (1988); B. Middleton, “Hydrochory, seed banks, and regeneration dynamics along the 

landscape boundaries of a forested wetland,” Plant Ecology 146:169-184 (2000); C. Nilsson, et 

al., “The role of hydrochory in structuring riparian and wetland vegetation,” Biological Reviews

85:837-858 (2010)).

Hydrological connections are often drivers of biological connections, and flooding events 

enhance the existing connections between floodplain waters and the river network. As a result, 

waters within floodplains have important functions for aquatic health. Many species have cycles 

timed to flooding events, particularly in circumstances where flooding is associated with annual 

spring snowmelt or high precipitation. Id. at 5-15 to 5-17, 5-20 (citing J.R. Thomas, et al., “A 
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landscape perspective of the stream corridor invasion and habitat characteristics of an exotic 

(Dioscorea oppositifolia) in a pristine watershed in Illinois,” Biological Invasions 8:1103-1113

(2006); L.M. Tronstad, et al., “Aerial colonization and growth: Rapid invertebrate responses to 

temporary aquatic habitats in a river floodplain,” Journal of the North American Benthological 

Society 26:460-471 (2007); A. Gurnell, et al., “Propagule deposition along river margins: 

Linking hydrology and ecology,” Journal of Ecology 96:553-565 (2008)). Waters within 

floodplains act as sinks of seeds, plant fragments, and invertebrate eggs, allowing for crossbreeding and resulting gene flow across time. Id. at 5-19 to 5-21 (citing K.M. Jenkins, and A.J. 

Boulton, “Connectivity in a dryland river: Short-term aquatic microinvertebrate recruitment 

following floodplain inundation,” Ecology 84:2708-2723 (2003); D. Frisch, and S.T. Threlkeld, 

“Flood-mediated dispersal versus hatching: Early recolonisation strategies of copepods in 

floodplain ponds,” Freshwater Biology 50:323-330 (2005); B. Vanschoenwinkel, et al., “Wind 

mediated dispersal of freshwater invertebrates in a rock pool metacommunity: Differences in 

dispersal capacities and modes,” Hydrobiologia 635:363-372 (2009)). Micro- and 

macroinvertebrates colonize nutrient rich waters within floodplains during periods of inundation, 

facilitating an increase in population and sustaining them though times of limited resources and 

population decline. Id. at 5-19 (citing W.J. Junk, et al., “The flood pulse concept in riverfloodplain systems,” in D.P. Dodge, ed., Proceedings of the International Large River 

Symposium Ottawa (Ottawa, Canada: Canadian Special Publication of Fisheries and Aquatic 

Sciences 106, 1989), pp. 110-127; B. Malmqvist, “Aquatic invertebrates in riverine landscapes,”

Freshwater Biology 47:679-694 (2002); C. Ilg, et al., “Long-term reactions of plants and 

macroinvertebrates to extreme floods in floodplain grasslands,” Ecology 89:2392-2398 (2008)). 

Such animals are adapted to high floods, desiccation (drying out), or other stresses that come 
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with these regular, systemic fluctuations. Id. at 5-20 (citing Jenkins and Boulton 2003). 

Floodplain waters therefore maintain various biological populations, which periodically 

replenish adjacent jurisdictional waters, serving to maintain their biological integrity. 

Plants and animals use waters, including wetlands, in the riparian areas and floodplains 

for habitat, food, and breeding. Oxbow lakes in the floodplain provide critical fish habitat 

needed for feeding and rearing, leading researchers to conclude that the entire floodplain should 

be considered a single functional unit, essential to the river’s biological integrity. Id. at 5-17

(citing D.E. Shoup and D.H. Wahl, “Fish Diversity and Abundance in Relation to Interannual 

and Lake- Specific Variation in Abiotic Characteristics of Floodplain Lakes of the Lower 

Kaskaskia River, Illinois,” Transactions of the American Fisheries Society 138:1076-1092

(2009)). Since adjacent ponds are structurally and biologically similar to oxbow lakes they serve 

similar functions relative to the nearby river or stream. Waters, including wetlands, in the 

riparian areas also provide food sources for stream invertebrates, which colonize during 

inundation events. Id. at 5-19 (citing W.J. Junk, et al., “The Flood Pulse Concept in RiverFloodplain Systems,” in D. P. Dodge, ed., Proceedings of the International Large River 

Symposium Ottawa (Ottawa, Canada: Canadian Special Publication of Fisheries and Aquatic 

Sciences 106, 1989), pp. 110-127; C. Ilg, et al., “Long-term Reactions of Plants and 

Macroinvertebrates to Extreme Floods in Floodplain Grasslands,” Ecology 89:2392-2398

(2008)). Riparian waters also form an integral part of the food web, linking primary producers 

and plants to higher animals. Id. (citing B. Malmqvist, “Aquatic Invertebrates in Riverine 

Landscapes,” Freshwater Biology 47:679-694 (2002); G.U.Y. Woodward and A.G. Hildrew, 

“Food Web Structure in Riverine Landscapes,” Freshwater Biology 47:777-798 (2002), T.K. 

Stead, et al., “Secondary Production of a Stream Metazoan Community: Does the Meiofauna 
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Make a Difference?,” Limnology and Oceanography 50:398-403 (2005), D.J. Woodford and 

A.R. McIntosh, “Evidence of Source-Sink Metapopulations in a Vulnerable Native Galaxiid Fish 

Driven by Introduced Trout,” Ecological Applications 20:967-977 (2010)). Likewise, floodplains 

are important foraging, hunting, and breeding sites for fish and amphibians. Id. at 5-15 (citing 

G.H. Copp, “The Habitat Diversity and Fish Reproductive Function of Floodplain Ecosystems,”

Environmental Biology of Fishes 26:1-27 (1989); J.S. Richardson, et al., “Riparian Communities 

Associated with Pacific Northwest Headwater Streams: Assemblages, Processes, and 

Uniqueness,” Journal of the American Water Resources Association 41:935-947 (2005)). 

Plants and animals move back and forth between riparian or floodplain waters and the 

river network. This movement is assisted in some cases when flooding events create hydrological 

connections. For instance, these floodplain and riparian wetlands provide refuge, feeding, and 

rearing habitat for many fish species. Id. at 5-17 (citing C.H. Wharton, et al., The Ecology of 

Bottomland Hardwood Swamps of the Southeast: A Community Profile, FWS/OBS-81/37

(Washington, D.C.: U.S. Department of the Interior, Fish and Wildlife Service, Biological 

Services Program, 1982); M.P. Matheney and C.F. Rabeni, “Patterns of Movement and Habitat 

Use by Northern Hogsuckers in an Ozark Stream,” Transactions of the American Fisheries 

Society 124:886-897 (1995); A.A. Pease, et al., “Habitat and Resource Use by Larval and 

Juvenile Fishes in an Arid-Land River (Rio Grande, New Mexico),” Freshwater Biology 51:475-

486 (2006); J.A. Henning, et al., “Use of Seasonal Freshwater Wetlands by Fishes in a 

Temperate River Floodplain,” Journal of Fish Biology 71:476-492 (2007); C.A. Jeffres, et al., 

“Ephemeral Floodplain Habitats Provide Best Growth Conditions for Juvenile Chinook Salmon 

in a California River,” Environmental Biology of Fishes 83:449-458 (2008)). Seeds ingested by 

animals such as carp are dispersed in stream channels and associated waters. See, e.g., id. at 5-16 
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(citing B.J.A. Pollux, et al., “Consequences of Intraspecific Seed-Size Variation in Sparganium 

emersum for Dispersal by Fish,” Functional Ecology 21:1084-1091 (2007)). Also, phytoplankton 

move between floodplain wetlands and the river network. Id. at 5-17 (citing D.G. Angeler, et al., 

“Phytoplankton community similarity in a semiarid floodplain under contrasting hydrological 

connectivity regimes,” Ecological Research 25:513-520 (2010)). In turn, the primary 

productivity conditions in the floodplain results in large populations of phytoplankton that enrich 

river networks when hydrological connections form. Id. (citing P.W. Lehman, et al., “The 

Influence of Floodplain Habitat on the Quantity and Quality of Riverine Phytoplankton Carbon 

Produced During the Flood Season in San Francisco Estuary,” Aquatic Ecology 42:363-378

(2008)). This influx of carbon into the river system nourishes the downstream waters, for 

example, supporting fisheries. 

However, even when hydrological connections are absent, some organisms can move 

between riparian waters and their neighboring tributaries by overland movement in order to 

complete their life cycle. River-dwelling mammals, such as river otters, move from the river to 

riparian wetlands. Id. at 5-18 (citing D.G. Newman and C.R. Griffin, “Wetland Use by River 

Otters in Massachusetts,” Journal of Wildlife Management 58:18-23 (1994)). Several species of 

amphibians and reptiles including frogs, snakes and turtles use both streams and neighboring 

waters. Id. at 1-10, 5-4 to 5-5 (Table 5-1), 5-15 (citing J.S. Richardson, et al., “Riparian 

Communities Associated with Pacific Northwest Headwater Streams: Assemblages, Processes, 

and Uniqueness,” Journal of the American Water Resources Association 41:935-947 (2005)). 

Movement between wetlands and the river network also occurs by the dispersal of seed and plant 

fragments and the wind dispersal of invertebrates. Id. at 5-15, 5-20 (citing R.L. Schneider and 

R.R. Sharitz, “Hydrochory and Regeneration in a Bald Cypress Water Tupelo Swamp Forest,”
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Ecology 69:1055-1063 (1988); B. Middleton, “Hydrochory, Seed Banks, and Regeneration 

Dynamics Along the Landscape Boundaries of a Forested Wetland,” Plant Ecology 146:169-184

(2000); A.M. Gurnell, “Analogies Between Mineral Sediment and Vegetative Particle Dynamics 

in Fluvial Systems,” Geomorphology 89:9-22 (2007); A. Gurnell, et al., “Propagule Deposition 

Along River Margins: Linking Hydrology and Ecology,” Journal of Ecology 96:553-565 (2008); 

C. Nilsson, et al., “The Role of Hydrochory in Structuring Riparian and Wetland Vegetation,”

Biological Reviews 85:837-858 (2010); L.M. Tronstad, et al., “Aerial Colonization and Growth: 

Rapid Invertebrate Responses to Temporary Aquatic Habitats in a River Floodplain,” Journal of 

the North American Benthological Society 26:460-471 (2007)). Animals, particularly migratory 

fish, may thus move between adjacent waters and (a)(1) through (a)(3) waters. And even when 

some species do not traverse the entire distance from adjacent waters to downstream waters, the 

downstream waters still benefit from the ecological integrity that persists because of the close 

relationship that adjacent waters have with nearby waters. This is because the chemical and 

biological properties that arise from interactions between adjacent waters and tributaries move 

downstream and support the integrity of (a)(1) through (a)(3) waters.

Biological connections between adjacent waters and river systems do not always increase 

with hydrologic connections. In some cases, the lack of connection improves the biological 

contribution provided by riparian waters towards neighboring streams, rivers, and lakes. For 

instance, the periodic hydrologic disconnectedness of oxbow lakes is necessary for the 

accumulation of plankton, an important source of carbon more easily assimilated by the aquatic 

food chain than terrestrial forms of carbon. Id. at 5-46 (citing C. Baranyi, et al., “Zooplankton 

Biomass and Community Structure in a Danube River Floodplain System: Effects of 

Hydrology,” Freshwater Biology 47:473-482 (2002); S. Keckeis, et al., “The Significance of 
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Zooplankton Grazing in a Floodplain System of the River Danube,” Journal of Plankton 

Research 25:243-253 (2003)). Similarly, some degree of hydrological disconnectedness is 

important in increasing the number of mollusk species and macroinvertebrate diversity in oxbow 

lakes, which in turn support the diversity of mollusks throughout the aquatic system. Id. at 5-46 

to 5-47 (citing W. Reckendorfer, et al., “Floodplain Restoration by Reinforcing Hydrological 

Connectivity: Expected Effects on Aquatic Mollusc Communities,” Journal of Applied Ecology

43:474-484 (2006); K. Obolewski, et al., “Effect of Hydrological Connectivity on the Molluscan 

Community Structure in Oxbow Lakes of the Lyna River,” Oceanological and Hydrobiological 

Studies 38:75-88 (2009).

2. Surface and Shallow Subsurface Hydrologic Connections Significantly Affect the 

Chemical, Physical, and Biological Integrity of (a)(1) through (a)(3) waters.

Wetlands and open waters, including those outside the riparian zone and floodplain, can 

be connected downstream through unidirectional flow from the wetland or open water to a 

nearby tributary. Many such connections are through a shallow subsurface hydrologic 

connection. Report at 3-7, 5-23. A shallow subsurface hydrologic connection is lateral water 

flow through a shallow subsurface layer, such as can be found in steeply sloping areas with 

shallow soils and soils with a restrictive horizon that prevents vertical water flow, or in karst 

systems. K.J. Devito, et al., “Groundwater-Surface Water Interactions in Headwater Forested 

Wetlands of the Canadian Shield,” Journal of Hydrology 181:127-47 (1996); M.A. O’Driscoll

and R.R. Parizek, “The Hydrologic Catchment Area of a Chain of Karst Wetlands in Central 

Pennsylvania, USA,” Wetlands 23:171-79 (2003); B.J. Cook and F.R. Hauer, “Effects of 

Hydrologic Connectivity on Water Chemistry, Soils, and Vegetation Structure and Function in 

an Intermontane Depressional Wetland Landscape,” Wetlands 27:719-38 (2007). Shallow 
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subsurface connections may be found below the ordinary root zone (below 12 inches), where 

other wetland delineation factors may not be present. The presence of an aquiclude (impervious 

layer) near the surface leads to shallow subsurface flows through the soil, which favors local 

groundwater flowpaths that connect to nearby wetlands or streams. Report at 3-38. 

Wetlands with shallow subsurface connections can affect the physical integrity of waters 

to which they connect. In general, the volume and sustainability of streamflow within river 

networks depends on contributions from groundwater, especially in areas with shallow 

groundwater tables and pervious (meaning water can easily pass through) subsurfaces. Id. at 3-12

(citing J.J. de Vries, “Seasonal Expansion and Contraction of Stream Networks in Shallow 

Groundwater Systems,” Journal of Hydrology 170:15-26 (1995); T.C. Winter, “The Role of 

Groundwater in Generating Streamflow in Headwater Areas and in Maintaining Base Flow,”

Journal of the American Water Resources Association 43:15-25 (2007); G.R. Kish, et al., “A 

Geochemical Mass-Balance Method for Base-Flow Separation, Upper Hillsborough River 

Watershed, West-Central Florida, 2003-2005 and 2009,” USGS Scientific Investigations Report 

2010–5092 (Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey, 2010). 

Because wetlands with shallow subsurface connections to streams and rivers provide some of 

these groundwater contributions, they influence the flow regime. Wetlands connected via 

shallow subsurface connections also can act as water sinks when evapotranspiration is high, but 

as water sources when evapotranspiration is low. Id. at 3-25. As a result, these adjacent waters 

moderate peak flows, reduce downstream flooding, and provide runoff to help maintain baseflow 

for streams during times of low flows. 

Wetlands and other waters with shallow subsurface connections affect the chemical and 

biological integrity of downstream waters in ways similar to wetlands with surface connections. 
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The distance between these wetlands and jurisdictional waters may influence the connectivity 

since wetlands with shorter distances to the stream network will have higher hydrological and 

biological connectivity than wetlands located further from the same network. Id. at 3-43. The 

distance between the wetland and water may also influence whether waters are connected via 

surface or shallow subsurface hydrologic connections. For wetlands connected to tributaries 

through groundwater flows, less distant wetlands/waters are generally connected through 

shallower flowpaths, assuming similar soil and geologic properties. Id. at 3-11 (Figure 3-5), 3-

42. These shallower groundwater flows have the greatest interchange with surface waters and 

travel between points in the shortest amount of time. Id. at 3-42. 

3. Adjacent Waters, Including Wetlands, Separated from Other Waters of the United 

States by Man-made Dikes or Barriers, Natural River Berms, Beach Dunes and the 

Like Significantly Affect the Chemical, Physical, and Biological Integrity of (a)(1) 

through (a)(3) Waters

The terms earthen dam, dike, berm, and levee are used to describe similar structures 

whose primary purpose is to help control flood waters. Such structures vary in scale and size. A 

levee is an embankment whose primary purpose is to furnish flood protection from seasonal high 

water and which is therefore subject to water loading for periods of only a few days or weeks a 

year. Earthen embankments that are subject to water loading for prolonged periods (longer than 

normal flood protection requirements) are called earth dams. There are a wide variety of types of 

structures and an even wider set of construction methods. These range from a poorly constructed, 

low earthen berm pushed up by a backhoe to a well-constructed, impervious core, riprap lined 

levee that protects houses and cropland. Generally, levees are built to detach the floodplain from 

the channel, decreasing overbank flood events. S.B. Franklin, et al., “Complex Effects of 
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Channelization and Levee Construction on Western Tennessee Floodplain Forest Function,” 

Wetlands 29(2): 451-464 (2009). The investigation methods to determine the presence or 

absence of the hydrologic connection depend on the type of structure, the underlying soils, the 

presence of groundwater, and the depth of the water table. Department of the Army, U.S. Army 

Corps of Engineers, Engineering and Design – Design and Construction of Levees, EM 1110-2-

1913 (Washington, D.C., Department of the Army, 2000), p. 1-1. 

Man-made berms and the like are fairly common along streams and rivers across the 

United States and often accompany stream channelization. S.B. Franklin, et al., “Complex 

Effects of Channelization and Levee Construction on Western Tennessee Floodplain Forest 

Function,” Wetlands 29(2): 451-464 (2009). One study conducted in Portland, Oregon found that

42% of surveyed wetlands had dams, dikes, or berms. M. Kentula, et al., “Tracking Changes in 

Wetlands with Urbanization: Sixteen Years of Experience in Portland, Oregon, USA,” Wetlands

24(4):734-743 (2004). Likewise, over 90% of the tidal freshwater wetlands of the SacramentoSan Joaquin Delta have been diked or leveed. C. Simenstad, et al., “Preliminary Results from the 

Sacramento-San Joaquin Delta Breached Levee Wetland Study,” Interagency Ecological 

Program for the Sacramento-San Joaquin Estuary Newsletter 12(4):15-21 (1999). At least 

40,000 kilometers of levees, floodwalls, embankments, and dikes are estimated across the United 

States, with approximately 17,000 kilometers of levees in the Upper Mississippi Valley alone. 

S.E. Gergel, et al., “Consequences of Human-altered Floods: Levees, Floods, and Floodplain 

Forests along the Wisconsin River,” Ecological Applications 12(6): 1755-1770 (2002).

Adjacent waters separated from the tributary network by dikes, levees, berms and the like 

continue to have a hydrologic connection to downstream waters. This is because berms and 

similar features typically do not block all water flow. Indeed, even dams, which as specifically 
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designed and constructed to impound large amounts of water effectively and safely, do not 

prevent all water flow, but rather allow seepage under the foundation of the dam and through the 

dam itself. See, e.g., International Atomic Energy Agency, Factsheet on Investigating Leaks 

through Dams and Reservoirs, 

http://www.tc.iaea.org/tcweb/publications/factsheets/sheet20dr.pdf ; U.S. Bureau of 

Reclamation, Provo Office, Safety of Dams, 

http://www.usbr.gov/uc/provo/progact/damsafety.html; Federal Energy Regulatory Commission 

(FERC), “Chapter 14: Dam Safety Performance Monitoring Program,” Engineering Guidelines 

for the Evaluation of Hydropower Projects (FERC, 2005), pp. 14-36 to 14-39. 

Seepage is the flow of a fluid through the soil pores. Seepage through a dam, through the 

embankments, foundations or abutments, or through a berm is a normal condition. D.A.Kovacic, 

et al., “Effectiveness of Constructed Wetlands in Reducing Nitrogen and Phosphorus Export 

from Agricultural Tile Drainage,” Journal of Environmental Quality 29(4): 1262-1274 (2000); 

Federal Energy Regulatory Commission (FERC), “Chapter 14: Dam Safety Performance 

Monitoring Program,” Engineering Guidelines for the Evaluation of Hydropower Projects 

(FERC, 2005), pp. 14-36 to 14-39. This is because water seeks paths of least resistance through 

the berm or dam and its foundation. Michigan Department of Environmental Quality, Seepage 

Through Earth Dams (2002), http://www.michigan.gov/deq/0,1607,7-135-3313_3684_3723-

9515--,00.html. All earth and rock-fill dams are subject to seepage through the embankment, 

foundation, and abutments. Department of the Army, U.S. Army Corps of Engineers, Seepage 

Analysis and Control for Dams, EM 1110-2-1901, (Washington, D.C.: Department of the Army, 

Original 1986 – Revised 1993), Page 1-1; Department of the Army, U.S. Army Corps of 

Engineers, Engineering and Design: General Design and Construction Considerations for Earth 
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and Rock-filled Dams, EM 1110-2-2300 (Washington, D.C.: Department of the Army, 2004), 

pp. 6-1 to 6-7. Concrete gravity and arch dams similarly are subject to seepage through the 

foundation and abutments. Department of the Army, U.S. Army Corps of Engineers, Seepage 

Analysis and Control for Dams, EM 1110-2-1901 (Washington, D.C.: Department of the Army, 

Original 1986 – Revised 1993), Page 1-1. Levees and the like are subject to breaches and breaks 

during times of floods. C. Nilsson, et al., “Fragmentation and Flow Regulation of the World’s 

Large River Systems,” Science 308(5720):405-408 (2005). Levees are similarly subject to failure 

in the case of extreme events, such as the extensive levee failures caused by Hurricanes Katrina 

and Rita. J.W. Day, et al., “Restoration of the Mississippi Delta: Lessons from Hurricanes 

Katrina and Rita,” Science 315(5819): 1679-1684 (2007). In designing levees and similar 

structures, seepage control is necessary to prevent possible failure caused by excessive uplift 

pressures, instability of the downstream slope, piping through the embankment and/or 

foundation, and erosion of material by migration into open joints in the foundation and 

abutments. Id.; D.A.Kovacic, et al., “Effectiveness of Constructed Wetlands in Reducing 

Nitrogen and Phosphorus Export from Agricultural Tile Drainage,” Journal of Environmental 

Quality 29(4): 1262-1274 (2000); U.S. Department of the Interior, Bureau of Reclamation, 

Upper Colorado Region, see http://www.usbr.gov/uc/provo/progact/damsafety.html; 

International Atomic Energy Agency, Investigating Leaks through Dams and Reservoirs, see 

http://www-tc.iaea.org/tcweb/publications/factsheets/sheet20dr.pdf; California Division of 

Safety of Dams, Embankment Design, see 

http://damsafety.water.ca.gov/guidelines/embankment.htm. 

The rate at which water moves through the embankment depends on the type of soil in 

the embankment, how well it is compacted, the foundation and abutment preparation, and the 
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number and size of cracks and voids within the embankment. All but the smallest earthen dams 

are commonly built with internal subsurface drains to intercept water seeping from the reservoir 

(i.e., upstream side) to the downstream side. Department of the Army, U.S. Army Corps of 

Engineers, Construction Control for Earth and Rock-filled Dams, EM 1110-2-1911, September 

30, 1995, Washington, D.C., 20314-1000, Page 1-1. Where it is not intercepted by a subsurface 

drain, the seepage will emerge downstream from or at the toe of the embankment. Michigan 

Department of Environmental Quality, Seepage Through Earth Dams (2002), 

http://www.michigan.gov/deq/0,1607,7-135-3313_3684_3723-9515--,00.html. Seepage may 

vary in appearance from a “soft,” wet area to a flowing “spring.” It may show up first as an area 

where the vegetation is lush and darker green. Cattails, reeds, mosses, and other marsh 

vegetation may grow in a seepage area. Michigan Department of Environmental Quality, 

Seepage Through Earth Dams (2002), http://www.michigan.gov/deq/0,1607,7-135-

3313_3684_3723-9515--,00.html.

Engineered berms are typically designed to interfere with the seasonal pattern of water 

level (hydroperiod) of the area behind the berm, reducing the frequency and severity of 

inundation. Berms are not designed to eliminate all hydrologic connection between the channel 

on one side and the area behind the berm on the other. It is almost always impracticable to build 

a berm that will not be overtopped by a flood of maximum severity, and most berms are not 

designed to withstand severe floods. See, e.g., Department of the Army, U.S. Army Corps of 

Engineers, Seepage Analysis and Control for Dams, EM 1110-2-1901, (Washington, D.C.: 

Department of the Army, Original 1986 – Revised 1993), Page 1-1. Levees are designed to allow 

seepage and are frequently situated on foundations having natural covers of relatively fine-grain 

impervious to semipervious soils overlying pervious sands and gravels. Department of the Army, 
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U.S. Army Corps of Engineers, Engineering and Design: Design Guidance for Levee 

Underseepage, ELT 1110-2-569, Washington, D.C.: Department of the Army, 2005), pp. 1-9. 

These surface strata constitute impervious or semipervious blankets when considered in 

connection with seepage. Principle seepage control measures for foundation underseepage are 

(a) cutoff trenches, (b) riverside impervious blankets, (c) landslide berms, (d) pervious toe 

trenches, and (e) pressure relief wells. Department of the Army, U.S. Army Corps of Engineers, 

Engineering and Design – Design and Construction of Levees, EM 1110-2-1913 (Washington, 

D.C., Department of the Army, 2000), p. 1-1. Overtopping of an embankment dam is very 

undesirable because the embankment materials may be eroded away. Additionally, only a small 

number of concrete dams have been designed to be overtopped. Water normally passes through 

the main spillway or outlet works; it should pass over an auxiliary spillway only during periods 

of high reservoir levels and high water inflow. All embankment and most concrete dams have 

some seepage. See, e.g.,

http://www.damsafety.org/layout/subsection.aspx?groupid=14&contentid=47. However, it is 

important to control the seepage to prevent internal erosion and instability. Proper dam 

construction, and maintenance and monitoring of seepage provide control. 

Berm-like landforms known as natural levees occur naturally and do not isolate adjacent 

wetlands from the streams that form them. Natural levees and the wetlands and waters behind 

them are part of the floodplain, including along some small streams and streams in the Arid 

West. C.A. Johnston, et al., “Nutrient Dynamics in Relation to Geomorphology of Riverine 

Wetlands,” Soil Science Society of America Journal 65(2):557-577 (2001). Every flowing 

watercourse transports not only water, but sediment—eroding and rebuilding its banks and 

floodplains continually. Federal Interagency Stream Restoration Working Group, Stream 
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Corridor Restoration: Principles, Processes and Practices, USDA National Engineering 

Handbook Part 653 (1999). Different deposition patterns occur under varying levels of 

streamflow, with higher flows having the most influence on the resulting shape of streambanks 

and floodplains. Id. In relatively flat landscapes drained by low-gradient streams, this natural 

process deposits the most sediment on the bank immediately next to the stream channel while 

floodplains farther from the channel are usually lower-lying wetlands (“backswamps” or 

“backwater wetlands”) that receive less sediment. See, e.g., C.A. Johnston, et al., “The Potential 

Role of Riverine Wetlands as Buffer Zones,” in N.E. Haycock, et al., ed., Buffer Zones Their 

Processes and Potential in Water Protection (Quest International, 1997), pp.155-170. The 

somewhat elevated land thus built up at streamside is called a natural levee, and this entirely 

natural landform is physically and hydrologically similar to narrow, man-made berms. See, e.g.,

L.B. Leopold, et al., Fluvial Processes in Geomorphology (Toronto: General Publishing Co. 

Ltd., 1964). Natural levees are discontinuous, which allows for a hydrologic connection to the 

stream or river via openings in the levees and thus the periodic mixing of river water and 

backwater. C.A. Johnston, et al., “Nutrient Dynamics in Relation to Geomorphology of Riverine 

Wetlands,” Soil Science Society of America Journal 65(2): 557-577 (2001). In addition, streams 

with natural levees, in settings with no human interference whatsoever, retain hydrologic 

connection with their wetlands behind the levees by periodic flooding during high water and via 

seepage through and under the levee. Similarly, man-made berms are typically periodically 

overtopped with water from the near-by stream, and as previously mentioned, are connected via 

seepage. 

Waters, including wetlands, separated from a stream by a natural or man-made berm 

serve many of the same functions as those discussed above on other adjacent waters. 
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Furthermore, even in cases where a hydrologic connection may not exist, there are other 

important considerations, such as chemical and biological factors, that result in a significant 

nexus between the adjacent wetlands or waters and the nearby waters of the United States, and 

(a)(1) through (a)(3) waters.

The movement of surface and subsurface both over berms and through soils and berms 

adjacent to rivers and streams is a hydrologic connection between wetlands and flowing 

watercourses. The intermittent connection of surface waters over top of, or around, natural and 

manmade berms further strengthens the evidence of hydrologic connection between wetlands 

and flowing watercourses. Both natural and man-made barriers can be topped by occasional 

floods or storm events. See, e.g., R.E. Turner, et al., “Wetland Sedimentation from Hurricanes 

Katrina and Rita,” Science 314(5798): 449-452 (2006); P.A. Keddy, et al., “The Wetlands of 

Lakes Pontchartrain and Maurepas: Past, Present and Future,” Environmental Reviews 15: 43-77 

(2007). When berms are periodically overtopped by water, wetlands and waters behind the 

barriers are directly connected to and interacting with the nearby stream and its downstream 

waters. In addition, surface waters move to and from adjacent soils (including adjacent wetland 

soils) continually. Along their entire length, streams alternate between effluent (water-gaining) 

and influent (water-losing) zones as the direction of water exchange with the streambed and 

banks varies. Federal Interagency Stream Restoration Working Group, Stream Corridor 

Restoration: Principles, Processes and Practices, USDA National Engineering Handbook Part 

653 (1999). The adjacent areas involved in this surface water exchange with a stream or river are 

known as the hyporheic zone. Hyporheic zone waters are part of total surface waters temporarily 

moving through soil or sediment. Like within-channel waters, these waters are oxygenated and 

support living communities of organisms in the hyporheic zone. 
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Because a hydrologic connection between adjacent wetlands and waters and downstream 

waters still exists despite the presence of a berm or the like, the chemical and biological 

connections that rely on a hydrologic connection also exist. For instance, adjacent waters behind 

berms can still serve important water quality functions, serving to filter pollutants and sediment 

before they reach downstream waters. Wetlands behind berms can function to filter pollutants 

before they enter the nearby tributary, with the water slowly released to the stream through 

seepage or other hydrological connections. See, e.g., L.L. Osborne and D.A. Kovacic, “Riparian 

Vegetated Buffer Strips in Water-Quality Restoration and Stream Management,” Freshwater 

Biology 29(2): 243-258 (1993); D.A. Kovacic, et al., “Effectiveness of Constructed Wetlands in 

Reducing Nitrogen and Phosphorus Export from Agricultural Tile Drainage,” Journal of 

Environmental Quality 29(4): 1262-1274 (2000). Their ability to retain sediment and floodwaters 

may be enhanced by the presence of the berm. For instance, some backwater wetlands in 

floodplain/riparian areas exhibit higher sedimentation rates than streamside locations. E.J. 

Kuenzler, et al., “Distributions and Budgets of Carbon, Phosphorus, Iron and Manganese in a 

Floodplain Swamp Ecosystem,” Water Resources Research Institute Report 157 (Chapel Hill, 

NC: University of North Carolina, 1980); C.A. Johnston, et al., “Nutrient Dynamics in Relation 

to Geomorphology of Riverine Wetlands,” Soil Science Society of America Journal 65(2): 557-

577 (2001). The presence of manmade levees can actually increase denitrification rates, meaning 

that the adjacent waters can more quickly transform nitrogen. S.E. Gergel, et al., “Do Dams and 

Levees Impact Nitrogen Cycling? Simulating the Effects of Flood Alterations on Floodplain 

Denitrification,” Global Change Biology 11(8): 1352-1367 (2005). However, the presence of 

manmade berms does limit the ability of the river to connect with its adjacent wetlands through 

overbank flooding and thus limits sediment, water and nutrients transported from the river to the 
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adjacent waters. Id.; J.L. Florsheim and J.F. Mount, “Changes in Lowland Floodplain 

Sedimentation Processes: Pre-disturbance to Post-rehabilitation, Cosumnes River, CA,” 

Geomorphology 56(3-4):305-323 (2003). However, the presence of a berm does not completely 

eliminate the transport of sediments and water from the river to the nearby adjacent wetland, as 

suspended sediments and water can overflow both natural and man-made levees, though the 

transport is usually more pronounced in settings with natural levees. See, e.g., R.E. Turner, et al., 

“Wetland Sedimentation from Hurricanes Katrina and Rita,” Science 314(5798):449-452 (2006); 

P.A. Keddy, et al., “The Wetlands of Lakes Pontchartrain and Maurepas: Past, Present and 

Future,” Environmental Reviews 15:43-77 (2007). Sediment deposition over levees is 

particularly enhanced by extreme events like hurricanes. Id.; D.J. Reed, et al., “Reducing the 

Effects of Dredged Material Levees on Coastal Marsh Function: Sediment Deposition and 

Nekton Utilization,” Environmental Management 37(5):671-685 (2006). Wetlands behind berms, 

where the system is extensive, can help reduce the impacts of storm surges caused by hurricanes. 

J.W. Day, et al., “Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina and 

Rita,” Science 315(5819):1679-1684 (2007). 

Adjacent waters, including wetlands, separated from water bodies by berms and the like 

maintain ecological connection with those water bodies. Though a berm may reduce habitat 

functional value and may prevent some species from moving back and forth from the wetland to 

the river, many major species that prefer habitats at the interface of wetland and stream 

ecosystems remain able to utilize both habitats despite the presence of such a berm. Additional 

species that are physically isolated in either stream or wetlands habitat still interact ecologically 

with species from the other component. Thus, adjacent wetlands with or without small berms can 

retain numerous similarities in ecological function. For example: wetland bird species such as 
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wading birds are able to utilize both wetland and adjacent stream/ditch habitats; wetland 

amphibians would be able to bypass the berm in their adult stage; aquatic invertebrates and fish 

would still interact with terrestrial/wetland predators and prey in common food web relationships 

despite the presence of a berm. See, e.g., G.S. Butcher, and B. Zimpel, “Habitat Value of Isolated 

Waters to Migratory Birds,” Prepared by Cornell Laboratory of Ornithology and The Cadmus 

Group, Inc. for U.S. Environmental Protection Agency Office of Wetlands Protection, 

(Washington, D.C.: Cornell and Cadmus, 1991); M.F. Willson and K.C. Halupka, “Anadromous 

Fish as Keystone Species in Vertebrate Communities,” Conservation Biology 9(3):489-497 

(1995); C.J. Cederholm, et al., “Pacific Salmon Carcasses: Essential Contributions of Nutrients 

and Energy for Aquatic and Terrestrial Ecosystems,” Fisheries 24(10):6-15 (1999); S.S. 

Schwartz and D.G. Jenkins, “Temporary Aquatic Habitats: Constraints and Opportunities,” 

Aquatic Ecology 34:3-8 (2000); D.T. Bilton, et al., “Dispersal in Freshwater Invertebrates,” 

Annual Review of Ecology and Systematics 32:159-81 (2001).

One example of adjacent waters behind berms and the like are interdunal wetlands 

located in coastal areas, including some areas of the Great Lakes and along barrier islands. 

Interdunal wetlands form in swales or depressions within open dunes or between beach ridges 

along the coast and experience a fluctuating water table seasonally and yearly in synchrony with 

sea or lake level changes. W.E. Odum, “Non-Tidal Freshwater Wetlands in Virginia,” Virginia 

Journal of Natural Resources Law 7: 421-434 (1988); D.A. Albert, Borne of the Wind: An 

Introduction to the Ecology of Michigan Sand Dunes (Lansing, MI: Michigan Natural Features 

Inventory, 2000), 63 pp.; D.A. Albert, Between Land and Lake: Michigan’s Great Lakes Coastal 

Wetlands, Bulletin E-2902 (East Lansing, MI: Michigan Natural Features Inventory, Michigan 

State University Extension, 2003), 96 pp; D.A. Albert, Natural Community Abstract for 
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Interdunal Wetland (Lansing, MI: Michigan Natural Features Inventory, 2007), 6 pp. For those 

along the ocean coast, they are typically formed as a result of oceanic processes where the 

wetlands establish behind relict dune ridges (dunes that were formed along a previously existing 

coast line). Wetlands in the interdunal system are in close proximity to each other and to the 

surrounding (a)(1) and/or (a)(3) waters. Their proximity to one another and to the (a)(1) and/or 

(a)(3) waters indicates a close physical relationship between interdunal wetland systems and the 

TNWs or territorial seas. Despite the presence of the beach dunes, interdunal wetlands have 

physical, chemical, and biological connections that greatly influence the integrity of the nearby 

(a)(1) and/or (a)(3) waters. The wetlands are hydrologically connected to these (a)(1) and/or 

(a)(3) waters through unconfined, directional flow and shallow subsurface flow during normal 

precipitation events and extreme events. As previously noted, they are linked to the rise and fall 

of the surrounding tides—the water-level fluctuations of the nearby a)(1) and/or (a)(3) waters are 

important for the dynamics of the wetlands. D.A. Albert, Between Land and Lake: Michigan’s 

Great Lakes Coastal Wetlands, Bulletin E-2902 (East Lansing, MI: Michigan Natural Features 

Inventory, Michigan State University Extension, 2003), 96 pp. The wetlands provide floodwater 

storage and attenuation, retaining and slowly releasing floodwaters before they reach the nearby 

(a)(1) and/or (a)(3) waters. Like other adjacent wetlands, interdunal wetlands also have important 

chemical connections to the nearby (a)(1) and/or (a)(3) waters, as they serve important water 

quality benefits. The wetlands store sediment and pollutants that would otherwise reach the 

surrounding (a)(1) and/or (a)(3) waters. The wetlands are biologically connected to the 

surrounding (a)(1) and/or (a)(3) waters. For instance, they provide critical habitats for species 

that utilize both the wetlands and the nearby (a)(1) and/or (a)(3) waters, supporting high diversity 

and structure. Habitat uses include basic food, shelter, and reproductive requirements. Aquatic 
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insects, amphibians, and resident and migratory birds all use interdunal wetlands as critical 

habitat, and the wetlands provide better shelter than the nearby exposed beach. D.A. Albert, 

Borne of the Wind: An Introduction to the Ecology of Michigan Sand Dunes (Lansing, MI: 

Michigan Natural Features Inventory, 2000), 63 pp.; S.M. Smith, et al., “Development of 

Vegetation in Dune Slack Wetlands of Cape Cod National Seashore (Massachusetts, USA),” 

Plant Ecology 194(2): 243-256 (2008). In marine coastal areas, the wetlands are often the only 

freshwater system in the immediate landscape, thus providing critical drinking water for the 

species that utilize both the wetlands and the nearby (a)(1) and/or (a)(3) waters, although some 

interdunal wetlands are brackish in nature. See, e.g., C.M. Heckscher and C.R. Bartlett, 

“Rediscovery and Habitat Associations of Photuris Bethaniensis McDermott (Coleoptera: 

Lampyridae),” The Coleopterists Bulletin 58(3): 349-353 (2004).

Wetlands behind the extensive levee system in the Yazoo Basin are an example of 

adjacent waters behind man-made barriers. A regional hydrogeomorphic approach guidebook for 

the Yazoo Basin of the Lower Mississippi River Alluvial Valley assesses the functions of these 

wetlands. R.D. Smith and C.V. Klimas, A Regional Guidebook for Applying the 

Hydrogeomorphic Approach to Assessing Wetland Functions of Selected Regional Wetland 

Subclasses, Yazoo Basin, Lower Mississippi River Alluvial Valle, Prepared for the U.S. Army 

Corps of Engineers, ERDC/EL TR-02-4 (2002). An extensive levee system was built along the 

river system to prevent flooding of the Mississippi River, resulting in drastic effects to the 

hydrology of the basin. Id. at 47. Despite the alteration of hydrology in the basin, extensive 

wetlands systems still exist behind the man-made and natural levees and maintain a hydrologic 

connection to the river system. These wetlands detain floodwater, detain precipitation, cycle 

nutrients, export organic carbon, remove elements and compounds, maintain plant communities, 
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and provide fish and wildlife habitat. Id. The functions in turn provide numerous and substantial 

benefits to the nearby river. 

4. Conclusions Regarding Adjacent Waters

The scientific literature documents that waters which are adjacent to (a)(1) through (a)(5) 

waters, including wetlands, oxbow lakes and adjacent ponds, are integral parts of tributary 

networks to (a)(1) through (a)(3) waters because they are directly connected to streams via 

permanent surface features that concentrate, mix, transform, and transport water and other 

materials, including food resources, downstream to larger rivers. Adjacent wetlands and other 

adjacent waters filter pollutants before they enter the tributary system, they attenuate flow during 

flood events, they regulate flow rate and timing, they trap sediment, and they input organic 

material into rivers and streams, providing the basic building blocks for their healthy 

functioning. These waters also are biologically connected to downstream waters by providing 

habitat and refuge to many species, and storing and releasing food sources. The scientific 

literature demonstrates that adjacent waters in a watershed together exert a strong influence on 

the character and functioning of rivers, streams and lakes. 

Adjacent waters, as defined, alone or in combination with other adjacent waters in a 

watershed, significantly affect the chemical, physical and biological integrity of traditional 

navigable waters, interstate waters, or the territorial seas. Based on studies of waters in riparian 

areas, flood plains, and hydrologic connections to the tributary system there is sufficient 

scientific evidence regarding the important functions of these adjacent wetlands to demonstrate 

that, alone or in combination with similarly situated waters in the region, wetlands and open 

waters adjacent to any tributary have a significant effect on the chemical, physical or biological 

integrity of traditional navigable waters, interstate waters, or the territorial seas. The reviewed 
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scientific literature supports the conclusion that adjacent waters generally play a larger role in the 

ecological condition of smaller tributary systems, which, in turn, determines the effects on the 

chemical, physical and biological health of larger downstream waters.

iii. “Other Waters”

The Report includes a focused evaluation of the connections and effects to downstream 

waters for several regional types of streams and wetlands: prairie streams, southwest intermittent 

and ephemeral streams, oxbow lakes, Carolina and Delmarva bays, prairie potholes, and vernal 

pools. These regional types were chosen for evaluation because they represent a broad 

geographic area as well as a diversity of water types based on their origin, landscape setting, 

hydrology, and other factors. Most prairie streams and southwest intermittent and ephemeral 

streams are likely to be considered tributaries to (a)(1) to (a)(3) waters (with the exception of 

streams, for example, located in closed basins, which lack an (a)(1) to (a)(3) water or a 

connection thereto); similarly, most oxbow lakes are likely to be considered adjacent to (a)(1) to 

(a)(5) waters. Carolina and Delmarva bays, prairie potholes, and vernal pools may or may not be 

considered adjacent to (a)(1) to (a)(5) waters. Where waters are not considered tributaries (e.g. 

waters in a solely intrastate closed basin that does not contain a traditional navigable water, 

interstate water, or a territorial sea, or a connection thereto) or where waters, including wetlands, 

do not meet the proposed regulatory definition of adjacent, they should be evaluated to determine 

whether they are (a)(7) waters. While the peer-reviewed published literature and the Report

contain documentation of functions provided by these “other waters,” as well as local factors that 

influence their degree of downstream connectivity, the agencies are not currently proposing to 
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establish any categories of “other waters” that are jurisdictional by rule without the necessity of a 

case-specific significant nexus standard. 

The term “other waters” refers to waters that cannot be considered “adjacent” to 

downstream jurisdictional waters and that are not tributaries of such waters. “Other waters” are 

found outside the riparian zone and the floodplain, as waters within these areas are considered to 

be “adjacent.” As such, wetlands that are “other waters” typically will have unidirectional flow. 

As mentioned in Part II, section 2.B. above, many unidirectional wetlands are considered 

adjacent and interact with downstream jurisdictional waters through channels, shallow 

subsurface flow, or by providing additional functions such as storage and mitigating peak flows. 

Unidirectional wetlands that lack a surface connection to downstream waters and are surrounded 

by uplands will typically fall under the definition of “other waters,” and are often referred to in 

scientific literature and policy as “geographically isolated waters.” The term “geographically 

isolated” should not be used to implicate the lack of connectivity to downstream waters, as these 

wetlands are often connected to downstream waters through shallow subsurface flow, biological 

connections, or spillage. The degree of connectivity of such wetlands will vary depending on 

landscape features such as distance from downstream waters and proximity to other wetlands of 

similar nature that as a group connect to jurisdictional downstream waters. Report at 3-43, 5-2.

For purposes of assessing whether a particular water is a water of the United States 

because it, alone or in combination with other similarly situated waters, has a significant nexus to 

an (a)(1) through (a)(3) water, the agencies are proposing to define each of the elements of 

Justice Kennedy’s significant nexus standard in the definition of “significant nexus.”

A. In the Region
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The agencies have determined that because the movement of water from watershed drainage 

basins to river networks and lakes shapes the development and function of these systems in a 

way that is critical to their long term health, the watershed is a reasonable and technically 

appropriate interpretation of Justice Kennedy’s standard. See, e.g., D.R. Montgomery, “Process 

Domains and the River Continuum,” Journal of the American Water Resources Association

35:397-410 (1999).

Using a watershed as the framework for conducting significant nexus evaluations is 

scientifically supportable. Watersheds are generally regarded as the most appropriate spatial unit 

for water resource management. See, e.g., J.M. Omernik and R.G. Bailey, “Distinguishing 

Between Watersheds and Ecoregions,” Journal of the American Water Resources Association

33.5: 939-40 (1997); D.R. Montgomery, “Process Domains and the River Continuum,” Journal 

of the American Water Resources Association 35: 397-410 (1999); T.C. Winter “The Concept of 

Hydrologic Landscapes,” Journal of the American Water Resources Association 37: 335-49 

(2001); J.S. Baron, et al., “Meeting Ecological and Societal Needs for Freshwater,” Ecological 

Applications 12: 1247-60 (2002); J.D. Allan, “Landscapes and Riverscapes: The Influence of 

Land Use on Stream Ecosystems,” Annual Review of Ecology Evolution and Systematics 35: 

257-84 (2004); United States, EPA 841-B-08-002: U.S. Environmental Protection Agency, 

Handbook for Developing Watershed Plans to Restore and Protect Our Waters: Planning & 

Implementation Steps (Washington D.C.: U.S. EPA, March 2008); P.J. Wigington, et al., 

“Oregon Hydrologic Landscapes: A Classification Framework,” Journal of the American Water 

Resources Association 49.1:163-82 (2013). Anthropogenic actions and natural events can have 

widespread effects within the watershed that collectively impact the quality of the relevant 

traditional navigable water, interstate water or territorial sea. United States, U.S. EPA and 
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USDA/ARS Southwest Watershed Research Center, EPA/600/R-08/134, ARS/2330462008: The 

Ecological and Hydrological Significance of Ephemeral and Intermittent Streams in the Arid and 

Semi-arid American Southwest (Washington, D.C.: U.S. EPA and USDA/ARS Southwest 

Watershed Research Center, Levick et al., 2008) (Levick, et. al.). For these reasons, it is more 

appropriate to conduct a significant nexus determination at the watershed scale than to focus on a 

specific site, such as an individual stream segment. The watershed size reflects the specific water 

management objective, and is scaled up or down as is appropriate to meet that objective. If the

objective is to manage the water quality in a particular receiving waterbody (the “target” 

waterbody), the watershed should include all those waters that are contributing to that target 

water since they will primarily determine the quality of the receiving water. 

The watershed that drains to the single point of entry to a traditional navigable water, 

interstate water or territorial sea is a logical spatial framework for the evaluation of the nexus. 

This is because, from a water quality management perspective, the (a)(1), (a)(2) or (a)(3) water is 

the downstream affected river or lake whose water quality that is dependent on the condition of 

the contributing upstream waters, including streams, lakes, and wetlands. To restore or maintain 

the health of the downstream affected river or lake, it is standard practice to evaluate the 

condition of the waters that are in the contributing watersheds and to develop a plan to address 

the issues of concern. The functions of the contributing waters are inextricably linked and have a 

cumulative effect on the integrity of the downstream traditional navigable water, interstate water 

or territorial sea. The size of that watershed can be determined by identifying the geographic 

area that drains to the nearest traditional navigable water or interstate water, and then using that 

point of entry watershed to conduct a significant nexus evaluation. P.E. Black, “Watershed 

Functions,” Journal of the American Water Resources Association 33.1:1-11 (1997). 
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The Corps is organized based on watersheds and has used framework approaches for 

water sources, navigation approaches for over 100 years, and in the regulatory program since its 

inception. Also, using a watershed framework is consistent with over two decades of practice by 

EPA and many other governmental, academic, and other entities which recognize that a 

watershed approach is the most effective framework to address water resource challenges. U.S. 

Environmental Protection Agency, The Watershed Protection Approach Framework (Oct. 1991).

The agencies both recognize the importance of the watershed approach by investing in 

opportunities to advance watershed protection and in developing useful watershed tools and 

services. For example, EPA is allowing States that are reorganizing programs to function on a 

watershed basis to have short-term backlogs on CWA Section 402 National Pollution Discharge 

Elimination System (NPDES) permit review -- without penalty. This flexibility gives States time 

to synchronize the reissuance of major and minor permits within a watershed. By managing 

NPDES permits on a watershed basis, all the permits for discharges to the waterbody can be 

coordinated and the most efficient and equitable allocation of pollution control responsibility can 

be made. U.S. Environmental Protection Agency, Why Watersheds?, EPA 800-F-96-001 

(February 1996). Applying a watershed approach continues to be a priority of EPA, and is one of 

the three key strategies the agency is using to drive progress toward the Agency’s health and 

environmental goals over the next five years. U.S Environmental Protection Agency, FY 2011-

2015 Strategic Plan: Achieving Our Vision, 2010. 

B. Similarly Situated 

Scientists routinely aggregate the effects of groups of waters, multiplying the known 

effect of one water by the number of similar waters in a specific geographic area, or to a certain 

scale. This kind of functional aggregation of non-adjacent (and other types of waters) is well-
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supported in the scientific literature. See, e.g., R.J. Stevenson and F.R. Hauer, “Integrating 

Hydrogeomorphic and Index of Biotic Integrity Approaches for Environmental Assessment of 

Wetlands,” Journal of the North American Benthological Society 21(3): 502-513 (2002); S.G. 

Leibowitz, “Isolated Wetlands and Their Functions: An Ecological Perspective,” Wetlands

23:517-531 (2003); D. Gamble, et al., An Ecological and Functional Assessment of Urban 

Wetlands in Central Ohio, Ohio EPA Technical Report WET/2007-3B (Columbus, OH: Ohio 

Environmental Protection Agency, 2007); C.R. Lane and E. D’Amico, “Calculating the 

Ecosystem Service of Water Storage in Isolated Wetlands using LiDAR in North Central Florida, 

USA,” Wetlands 30:967–977 (2010); B.P. Wilcox, et al., “Evidence of Surface Connectivity for 

Texas Gulf Coast Depressional Wetlands,” Wetlands 31(3):451-8 (2011). Similarly, streams and 

rivers are routinely aggregated by scientists to estimate their combined effect on downstream 

waters in the same watershed. This is because chemical, physical, or biological integrity of 

downstream waters is directly related to the aggregate contribution of upstream waters that flow 

into them, including any tributaries and connected wetlands. As a result, the scientific literature 

and the Report consistently documents that the health of larger downstream waters is directly 

related to the aggregate health of waters located upstream, including waters such as wetlands that 

may not be hydrologically connected but function together to prevent floodwaters and 

contaminants from reaching downstream waters. 

In the aggregate, similarly situated wetlands may have significant effects on the quality of 

water many miles away, particularly in circumstances where numerous similarly situated waters 

are located in the same region and are performing like functions that combine to influence 

downstream waters. See, e.g., A. Jansson et al., “Quantifying the Nitrogen Retention Capacity of 

Natural Wetlands in the Large-Scale Drainage Basin of the Baltic Sea,” Landscape Ecology
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13:249-262 (1998); W.J. Mitsch et al., “Reducing Nitrogen Loading to the Gulf of Mexico from 

the Mississippi River Basin: Strategies to Counter a Persistent Ecological Problem,” BioScience

51(5): 373-388 (2001); M.G. Forbes, et al., “Nutrient Transformation and Retention by Coastal 

Prairie Wetlands, Upper Gulf Coast, Texas,” Wetlands 32(4):705-15 (2012). Cumulatively, many 

small wetlands can hold a large amount of snowmelt and precipitation, reducing the likelihood of 

flooding downstream. Report at 5-25 (citing D.E. Hubbard and R.L. Linder, “Spring Runoff 

Retention in Prairie Pothole Wetlands,” Journal of Soil and Water Conservation 41(2):122-125 

(1986)). 

Scientists can and do routinely classify similar waters and wetlands into groups for a 

number of different reasons; because of their inherent physical characteristics, because they 

provide similar functions, because they were formed by similar geomorphic processes, and by 

their level of biological diversity, for example. Classifying wetlands based on their functions is 

also the basis for the U.S. Army Corps of Engineers hydrogeomorphic (HGM) classification of 

wetlands. M.M. Brinson, A Hydrogeomorphic Classification for Wetlands (Washington, D.C.: 

U.S. Army Corps of Engineers, 1993). The HGM method is a wetlands assessment approach 

pioneered by the Corps in the 1990s, and extensively applied via regional handbooks since then. 

The Corps HGM method uses a conceptual framework for identifying broad wetland classes 

based on common structural and functional features, which includes a method for using local 

attributes to further subdivide the broad classes into regional subclasses. Assessment methods 

like the HGM provide a basis for determining if waters provide similar functions based on their 

structural attributes and indicator species. Scientists also directly measure attributes and 

processes taking place in particular types of waters during in-depth field studies that provide 
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reference information that informs the understanding of the functions performed by many types 

of aquatic systems nationwide. 

These waters, primarily depressional wetlands, small open waters and peatlands, are 

known to have important hydrologic, water quality, and habitat functions which vary as a result 

of the diverse settings in which they exist across the country. For example, a report that reviewed 

the results of multiple scientific studies concluded that depressional wetlands lacking a surface 

outlet functioned together to significantly reduce or attenuate flooding. Report at 5-26 (citing A. 

Bullock and M. Acreman, “The Role of Wetlands in the Hydrological Cycle,” Hydrology and 

Earth System Sciences 7:358-389 (2003)). Some of the important factors which influence the 

variability of their functions and connectivity include the topography, geology, soil features, 

antecedent moisture conditions, and seasonal position of the water table relative to the wetland. 

Report at 5-25.

When proposing that “other waters” are sufficiently close and should be considered 

similarly situated, it is recognized that they are more likely to have similar influence with regard 

to their effect on the chemical, physical, or biological integrity of a downstream water identified 

in paragraphs (a)(1) through (a)(3)). If a water is a great distance from a group of similar “other 

waters,” it may be performing some of the same functions as those in the group, but their 

distance from each other or from downstream (a)(1) through (a)(3) waters will decrease the 

probability that it has some kind of chemical, physical, or biological connectivity to the 

downstream water, assuming that conditions governing the type and quantity of flows (e.g. slope, 

soil, and aquifer permeability, etc) are similar. Id. at 5-2, 5-41. 

Consideration of the aggregate effects of wetlands and other waters often gives the most 

complete information about how such waters influence the chemical, physical, and biological 
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integrity of downstream waters. In many watersheds, wetlands have a disproportionate effect on 

water quality relative to their surface area because wetland plants slow down water flow, 

allowing suspended sediments, nutrients, and pollutants to settle out. They filter these materials 

out of the water received from large areas, absorbing or processing them, and then releasing 

higher quality water. National Research Council, Wetlands: Characteristics and Boundaries

(Washington, D.C.: National Academy Press, 1995), p. 38. For an individual wetland, this is 

most pronounced where it lies immediately upstream of a drinking water intake, for example. 

See, e.g., C.A. Johnston, et al., “The Cumulative Effect of Wetlands on Stream Water Quality 

and Quantity,” Biogeochemistry 10:105-141 (1990).

The structure and function of a river are highly dependent on the constituent materials 

that are stored in, or transported through the river. Most of the materials found in rivers originate 

outside of them. Thus, the fundamental way that “other waters” are able to affect river structure 

and function is by providing or altering the materials delivered to the river. Report at 1-13. Since 

the alteration of material fluxes depends on the functions within these waters and the degree of 

connectivity, it is appropriate to consider both these factors for purposes of significant nexus 

under this provision.

Numerous factors affect chemical, physical, and biological connectivity, operating at 

multiple spatial and temporal scales, and interacting with each other in complex ways, to 

determine where components of aquatic systems fall on the connectivity-isolation gradient at a 

given time. Some of these factors include climate, watershed characteristics, spatial distribution 

patterns, biota, and human activities and alterations. Id. at 3-33. Recognizing the limits on the

ability to observe or document all of these interacting factors, it is reasonable to look for visible 

patterns in the landscape and waters that are often indicative of the connectivity factors, in 
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determining what waters to aggregate. Due to relative similarity of soils, topography, or 

groundwater connections, for example, there may be a group of wetlands scattered throughout a 

watershed, at similar distances from the tributaries in the watershed and performing similar 

functions. It is appropriate to assess the significance of the nexus of those waters in the 

aggregate, consistent with Justice Kennedy’s standard.

C. Significant Nexus

The scientific literature regarding “other waters” documents their functions, including the 

chemical, physical, and biological impact they can have downstream. Available literature

indicates that “other waters” have important hydrologic, water quality, and habitat functions that 

have the ability to affect downstream waters if and when a connection exists between the “other

water” and downstream waters. Report at 6-1. “Other waters” generally fit into the category of 

unidirectional waters as described in the Report. However, there are some unidirectional waters 

that are in fact adjacent under (a)(6) to (a)(1) through (a)(5) waters (e.g., neighboring waters that 

are outside of the riparian area and/or floodplain but that have a surface or shallow subsurface 

hydrologic connection to (a)(1) through (a)(5) waters). Connectivity of “other waters” to 

downstream waters that do not meet the definition of adjacent will vary within a watershed and 

over time, which is why a case-specific significant nexus determination for “other waters” is 

necessary under (a)(7). See, e.g., id. at 6-2. The types of chemical, physical, and biological 

connections between “other waters” and downstream waters are described below for illustrative 

purposes. As described in the preamble above, when the agencies are conducting a case-specific 

determination for significant nexus under (a)(7), they examine the connections between the water 

(including any similarly situated waters in the region) and downstream waters and determine if 

those connections significantly affect the chemical, physical, or biological integrity of the 
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downstream water, using any available site-information and field observations where available, 

relevant scientific studies or data, or other relevant jurisdictional determinations that have been 

made on similar resources in the region. 

The hydrologic connectivity of “other waters” to downstream waters occurs on a gradient 

and can include waters that have groundwater or occasional surface water connections (through 

overland flow) to the tributary network and waters that have no hydrologic connection to the 

tributary network. Id. at 5-1. The connectivity of “other waters” to downstream waters will vary 

within a watershed as a function of local factors (e.g. position, topography, and soil 

characteristics). Id. at 3-41 to 3-43. Connectivity also varies over time, as the tributary network 

and water table expand and contract in response to local climate. Id. at 3-31 to 3-33. Lack of 

connection does not necessarily translate to lack of impact; even when lacking connectivity, 

waters can still impact chemical, physical, and biological conditions downstream. Id. at 3-29, 3-

31.

The physical effect that “other waters” have downstream is less obvious than the physical 

connections of waters that are adjacent or waters that are tributary, due to the physical distance 

of “other waters” from the stream network. Despite this physical distance, they are frequently 

connected in some degree through either surface water or groundwater systems; over time, 

impacts in one part of the hydrologic system will be felt in other parts. T.C. Winter and J.W. 

LaBaugh, “Hydrologic Considerations in Defining Isolated Wetlands,” Wetlands 23:532-540 

(2003) at 538. For example, “other waters” that overspill into downstream waterbodies during 

times of abundant precipitation are connected over the long term. Id. at 539. Wetlands that lack 

surface connectivity in a particular season or year can, nonetheless, be highly connected in wetter 

seasons or years. Report at 5-22 to 5-25. Many “other waters” interact with groundwater, either 
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by receiving groundwater discharge (flow of groundwater to the “other water”), contributing to 

groundwater recharge (flow of water from the “other water” to the groundwater), or both. Id. at 

5-23 (citing R.F. Lide, et al., “Hydrology of a Carolina Bay Located on the Upper Coastal Plain 

of Western South Carolina,” Wetlands 15:47-57 (1995); K.J. Devito, et al., “Groundwater 

Surface-Water Interactions in Headwater Forested Wetlands of the Canadian Shield,” Journal of 

Hydrology 181:127-47 (1996); R.K. Matheney and P.J. Gerla, “Environmental Isotopic Evidence 

for the Origins of Ground and Surface Water in a Prairie Discharge Wetland,” Wetlands 16:109-

120 (1996); D.O. Rosenberry and T.C. Winter, “Dynamics of Water-Table Fluctuations in an 

Upland between Two Prairie-Pothole Wetlands in North Dakota,” Journal of Hydrology

191:266-289 (1997); J.E. Pyzoha, et al., “A Conceptual Hydrologic Model for a Forested 

Carolina Bay Depressional Wetland on the Coastal Plain of South Carolina, USA,” Hydrological 

Processes 22:2689-2698 (2008)). Factors that determine whether a water recharges groundwater 

or is a site of groundwater discharge include topography, geology, soil features, and seasonal 

position of the water table relative to the water. Id. at 5-24 (citing P.J. Phillips and R.J. 

Shedlock, “Hydrology and Chemistry of Groundwater and Seasonal Ponds in the Atlantic 

Coastal-Plain in Delaware, USA,” Journal of Hydrology 141:157-78 (1993); R.J. Shedlock, et 

al., “Interactions between Ground-Water and Wetlands, Southern Shore of Lake-Michigan, 

USA,” Journal of Hydrology 141:127-55 (1993); D.O. Rosenberry and T.C. Winter, “Dynamics 

of Water-Table Fluctuations in an Upland Between two Prairie-Pothole Wetlands in North 

Dakota,” Journal of Hydrology 191:266-89 (1997); J.E. Pyzoha, et al., “A Conceptual 

Hydrologic Model for a Forested Carolina Bay Depressional Wetland on the Coastal Plain of 

South Carolina, USA,” Hydrological Processes 22: 2689-98 (2008)). Similarly, the magnitude 

and transit time of groundwater flow from an “other water” to downstream waters depend on 
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several factors, including the intervening distance and the properties of the rock or 

unconsolidated sediments between the waterbodies (i.e., the hydraulic conductivity of the 

material). Id. at 5-24. Surface and groundwater hydrological connections are those generating the 

capacity for “other waters” to affect downstream waters, as water from the “other water” may 

contribute to baseflow or stormflow through groundwater recharge. Id. at 5-25. Contributions to 

baseflow are important for maintaining conditions that support aquatic life in downstream 

waters. As discussed further below, even in cases where waters lack a connection to downstream 

waters, they can influence downstream water through water storage and mitigation of peak 

flows. Id. at 5-36.

The chemical effects that “other waters” have on downstream waters are linked to their 

hydrologic connection downstream, though a surface connection is not needed for a water to 

influence the chemical integrity of the downstream water. Because the majority of “other waters”

are hydrologically connected to downstream waters via surface or groundwater connections, 

most “other waters” can affect water quality downstream (although these connections do not 

meet the definition of adjacency). D.F. Whigham and T. E. Jordan, “Isolated Wetlands and 

Water Quality,” Wetlands 23:541-549 (2003) at 542. “Other waters” can act as sinks and 

transformers for nitrogen and phosphorus, metals, pesticides, and other contaminants that could 

otherwise negatively impact downstream waters. Report at 5-30 (citing R.R. Brooks, et al., 

“Cobalt and Nickel Uptake by the Nyssaceae,” Taxon 26:197-201 (1977); H.F. Hemond, 

“Biogeochemistry of Thoreau’s Bog, Concord, Massachusetts,” Ecological Monographs 50:507-

526 (1980); C.B. Davis, et al., “Prairie Pothole Marshes as Traps for Nitrogen and Phosphorus in 

Agricultural Runoff,” in B. Richardson, ed., Selected Proceedings of the Midwest Conference on 

Wetland Values and Management, June 17-19, 1981, St. Paul, MN, (St. Paul, MN: The 
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Freshwater Society, 1981), pp. 153-163; H.F. Hemond, “The Nitrogen Budget of Thoreau’s 

Bog,” Ecology 64:99-109 (1983); K.C. Ewel and H.T. Odum, ed., Cypress Swamps, (Gainesville, 

Florida: University of Florida Press, 1984); J.T. Moraghan, “Loss and Assimilation of 15Nnitrate Added to a North Dakota Cattail Marsh,” Aquatic Botany 46:225-234 (1993); C.M. Kao, 

et al., “Non-point Source Pesticide Removal by a Mountainous Wetland,” Water Science and 

Technology 46:199-206 (2002); P.I. Boon, “Biogeochemistry and Bacterial Ecology of 

Hydrologically Dynamic Wetlands,” in D.P. Batzer and R.R. Sharitz, ed., Ecology of Freshwater 

and Estuarine Wetlands (Berkeley, CA: University of California Press, 2006), pp. 115-176; E.J. 

Dunne, et al., “Phosphorus Release and Retention by Soils of Natural Isolated Wetlands,” 

International Journal of Environment and Pollution 28:496-516 (2006); T.E. Jordan, et al., 

“Comparing Functional Assessments of Wetlands to Measurements of Soil Characteristics and 

Nitrogen Processing,” Wetlands 27:479-497 (2007); S.L. Whitmire and S.K. Hamilton, “Rates of 

Anaerobic Microbial Metabolism in Wetlands of Divergent Hydrology on a Glacial Landscape,” 

Wetlands 28:703-714 (2008)). Also see, e.g., T.M. Isenhart, Transformation and Fate of Nitrate 

in Northern Prairie Wetlands, Ph.D. Dissertation (Ames, Iowa: Iowa State University, 1992).

The body of published scientific literature and the Report indicate that sink removal of nutrients 

and other pollutants by “other waters” is significant and geographically widespread. Report at 5-

30. Water quality characteristics of “other waters” are highly variable, depending primarily on 

the sources of water, characteristics of the substrate, and land uses within the watershed. D.F. 

Whigham and T.E. Jordan, “Isolated Wetlands and Water Quality,” Wetlands 23:541-549 (2003)

at 541. These variables inform whether an “other water” has a significant nexus to an (a)(1) to 

(a)(3) water. For instance, some prairie potholes may improve water quality and may efficiently 

retain nutrients that might otherwise cause water quality problems downstream; in such systems 
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it may be their lack of a direct hydrologic connection that enables the prairie potholes to more 

effectively retain nutrients. Id. at 543. 

“Other waters” can be biologically connected to each other and to downstream waters 

through the movement of seeds, macroinvertebrates, amphibians, reptiles, birds, and mammals. 

Report at 5-31 to 5-33; S.G. Leibowitz, “Isolated Wetlands and Their Functions: An Ecological 

Perspective,” Wetlands 23:517-531 (2003) at 519. The movement of organisms between “other 

waters” and downstream waters is governed by many of the same factors that affect movement 

of organisms between adjacent wetlands and downstream waters (See Part II Section 2.A.d.). 

Report at 5-31. Generally, “other waters” are further away from stream channels than adjacent 

waters, making hydrologic connectivity less frequent, and increasing the number and variety of 

landscape barriers over which organisms must disperse. Id. Plants, though non-mobile, have 

evolved many adaptations to achieve dispersal over a variety of distances, including water-borne 

dispersal during periodic hydrologic connections, “hitchhiking” on or inside highly mobile 

animals, and more typically via wind dispersal of seeds and/or pollen. Id. at 5-31 (citing S.M. 

Galatowitsch and A.G. van der Valk, “The Vegetation of Restored and Natural Prairie 

Wetlands,”Ecological Applications 6:102-112 (1996); H.R. Murkin and P.J. Caldwell, “Avian 

Use of Prairie Wetlands,” in H.R. Murkin, et al., ed., Prairie Wetland Ecology: The 

Contribution of the Marsh Ecology Research Program, (Ames, IA: Iowa State University Press, 

2000), pp. 249-286; J.M. Amezaga, et al., “Biotic Wetland Connectivity - Supporting a New 

Approach for Wetland Policy,” Acta Oecologica-International Journal of Ecology 23:213-222 

(2002); J. Figuerola and A.J. Green, “Dispersal of Aquatic Organisms by Waterbirds: a Review 

of Past Research and Priorities for Future Studies,” Freshwater Biology 47:483-494 (2002); 

M.B. Soons and G.W. Heil, “Reduced Colonization Capacity in Fragmented Populations of 
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Wind-Dispersed Grassland Forbs,” Journal of Ecology 90:1033-1043 (2002); M.B. Soons, 

“Wind Dispersal in Freshwater Wetlands: Knowledge for Conservation and Restoration,” 

Applied Vegetation Science 9:271-278 (2006); C. Nilsson, et al., “The Role of Hydrochory in 

Structuring Riparian and Wetland Vegetation,” Biological Reviews 85:837-858 (2010)). 

Mammals that disperse overland can also contribute to connectivity and can act as transport 

vectors for hitchhikers such as algae. Id. at 5-32 (citing C.E. Shanks and G.C. Arthur, “Muskrat 

Movements and Population Dynamics in Missouri Farm Ponds and Streams,” Journal of Wildlife 

Management 16:138-148 (1952); J.P. Roscher, “Alga Dispersal by Muskrat Intestinal Contents,” 

Transactions of the American Microscopical Society 86:497-498 (1967); W.R. Clark, “Ecology 

of Muskrats in Prairie Wetlands,” in H. R. Murkin, et al., ed., 2000, pp. 287-313)). Invertebrates 

also utilize birds and mamals to hitchhike, and these hitchhikers can be an important factor 

structuring invertebrate metapopulations in “other waters” and in aquatic habitats separated by 

hundreds, or potentially, thousands of kilometers. Id. (citing J. Figuerola and A.J. Green, 

“Dispersal of Aquatic Organisms by Waterbirds: A Review of Past Research and Priorities for 

Future Studies,” Freshwater Biology 47:483-494 (2002); J. Figuerola, et al., “Invertebrate Eggs 

Can Fly: Evidence of Waterfowl-Mediated Gene Flow in Aquatic Invertebrates,” American 

Naturalist 165:274-280 (2005); M.R. Allen, “Measuring and Modeling Dispersal of Adult 

Zooplankton,” Oecologia 153:135-143 (2007); D. Frisch, et al., “High Dispersal Capacity of a 

Broad Spectrum of Aquatic Invertebrates Via Waterbirds,” Aquatic Sciences 69:568-574 (2007)). 

Numerous flight-capable insects use both “other waters” and downstream waters; these insects 

move outside the tributary network to find suitable habitat for overwintering, refuge from 

adverse conditions, hunting, foraging, or breeding, and then can return back to the tributary 

network for other lifecycle needs. Id. at 5-33 (citing D.D. Williams, “Environmental Constraints 
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in Temporary Fresh Waters and Their Consequences for the Insect Fauna,” Journal of the North 

American Benthological Society 15:634-650 (1996); A.J. Bohonak and D.G. Jenkins, 

“Ecological and Evolutionary Significance of Dispersal by Freshwater Invertebrates,” Ecology 

Letters 6:783-796 (2003)). Amphibians and reptiles also move between “other waters” and 

downstream waters to satisfy part of their life history requirements. Id. at 5-33. Alligators in the 

Southeast, for instance, can move from tributaries to shallow, seasonal limesink wetlands for 

nesting, and also use these wetlands as nurseries for juveniles; sub-adults then shift back to the 

tributary network through overland movements. Id. (citing A.L. Subalusky, et al., “Ontogenetic 

Niche Shifts in the American Alligator Establish Functional Connectivity between Aquatic 

Systems,” Biological Conservation 142:1507-1514 (2009); A.L. Subalusky, et al., “Detection of 

American Alligators in Isolated, Seasonal Wetlands,” Applied Herpetology 6:199-210 (2009)). 

Similarly, amphibians and small reptile species, such as frogs, toads, and newts, commonly use 

both tributaries and “other waters,” during one or more stages of their life cycle, and can at times 

disperse over long distances. Id. (citing V.S. Lamoureux and D.M. Madison, “Overwintering 

Habitats of Radio-Implanted Green Frogs, Rana clamitans,” Journal of Herpetology 33:430-435 

(1999); K.J. Babbitt, et al., “Patterns of Larval Amphibian Distribution along a Wetland 

Hydroperiod Gradient,” Canadian Journal of Zoology-Revue Canadienne De Zoologie 81:1539-

1552 (2003); S.B. Adams, et al., “Instream Movements by Boreal Toads (Bufo boreas boreas),” 

Herpetological Review 36:27–33 (2005); D.M. Green, “Bufo americanus, American Toad,” in 

M. Lannoo, ed., Amphibian Declines: The Conservation Status of the United States Species

(Berkeley, CA: University of California Press, 2005), pp. 692-704; T.W. Hunsinger and M. J. 

Lannoo, “Notophthalmus viridescens, Eastern Newt,” in M. Lannoo, ed., 2005, pp. 912-914; 

J.W. Petranka and C.T. Holbrook, “Wetland Restoration for Amphibians: Should Local Sites Be 
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Designed to Support Metapopulations or Patchy Populations?,” Restoration Ecology 14:404-411 

(2006)).

Even when a surface or groundwater hydrologic connection between a water and a 

downstream water is visibly absent, many waters still have the ability to substantially influence 

the integrity of downstream waters. However, such circumstances would be uncommon. Id. at 5-

22 to 5-25. Aquatic systems that may seem disconnected hydrologically are often connected but 

at irregular timeframes or through subsurface flow, and perform important functions that can be 

vital to the chemical, physical or biological integrity of downstream waters. Some wetlands that 

are not adjacent may be hydrologically disconnected most of the time but connected to the 

stream network during rare high-flow events. The lack of a hydrologic connection also allows for 

water storage in “other waters,” attenuating peak streamflows, and, thus, downstream flooding, 

and also reducing nutrient and soil pollution in downstream waters. Report at 5-25 to 5-26, 5-36. 

Prairie potholes a great distance from any tributary, for example, are thought to store significant 

amounts of runoff. Id. at 5-36 (citing R.P. Novitzki, “Hydrologic Characteristics of Wisconsin’s 

Wetlands and Their Influence on Floods,” in P. Greeson, et al., ed., Wetland Functions and 

Values: The Status of Our Understanding, Proceedings of the National Symposium on Wetlands 

(Minneapolis, MN: American Water Resources Association, 1979), pp. 377-388; D.E. Hubbard 

and R.L. Linder, “Spring Runoff Retention in Prairie Pothole Wetlands,” Journal of Soil and 

Water Conservation 41:122-125 (1986); J. Jacques and D.L. Lorenz, “Techniques for Estimating 

the Magnitude and Frequency of Floods in Minnesota,” Water Resources Investigations Report

87-4170, (St. Paul, MN: U.S. Geological Survey, 1988); K.C. Vining, “Simulation of 

Streamflow and Wetland Storage, Starkweather Coulee Subbasin, North Dakota, Water Years 

1981-98,” Water-Resources Investigations Report 02-4113 (Bismarck, North Dakota: U.S. 
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Geological Survey, 2002); R.A. Gleason, et al., Estimating Water Storage Capacity of Existing 

and Potentially Restorable Wetland Depressions in a Subbasin of the Red River of the North, 

U.S. Geological Survey Open-File Report 2007-1159 (Reston, VA: U.S. Geological Survey, 

2007); D.L. Lorenz, et al., “Techniques for Estimating the Magnitude and Frequency of Peak 

Flows on Small Streams in Minnesota Based on Through Water Year 2005,” USGS Scientific 

Investigations Report 2009-5250, (Reston, VA: U.S. Geological Survey, 2010)). Filling wetlands 

reduces water storage capacity in the landscape and causes runoff from rainstorms to overwhelm 

the remaining available water conveyance system. See, e.g., C.A. Johnston, et al., “The 

Cumulative Effect of Wetlands on Stream Water Quality and Quantity,” Biogeochemistry 

10:105-141 (1990); A.L. Moscrip and D.R. Montgomery, “Urbanization, Flood Frequency, and 

Salmon Abundance in Puget Lowland Streams,” Journal of the American Water Resources 

Association 33:1289-1297 (1997); N.E. Detenbeck, et al., “Evaluating Perturbations and 

Developing Restoration Strategies for Inland Wetlands in the Great Lakes Basin,” Wetlands

19(4): 789-820 (1999); N.E. Beck, et al., “Relationship of Stream Flow Regime in the Western 

Lake Superior Basin to Watershed Type Characteristics,” Journal of Hydrology 309(1-4): 258-

276 (2005). Wetlands, even when lacking a hydrologic connection downstream, improve 

downstream water quality by accumulating nutrients, trapping sediments, and transforming a 

variety of substances. See, e.g., National Research Council, Wetlands: Characteristics and 

Boundaries (Washington, D.C.: National Academy Press, 1995), p. 38. 

As examples, the Report includes case studies of the chemical, physical, and biological 

connections that Carolina and Delmarva Bays, prairie potholes, and vernal pools have with 

downstream waters. These waters may fit into the category of “other waters” where they do not 
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qualify as either tributary waters or adjacent waters. A brief summary of the findings of each 

case study follows below.

Carolina and Delmarva bays are elliptical-shaped, ponded depressional wetlands located 

along the Atlantic Coastal Plain from Northern Florida to New Jersey. Report at 5-49 (citing 

W.F. Prouty, “Carolina Bays and Their Origin,” Bulletin of the Geological Society of America

63:167-224 (1952); D.D. Williams, “Environmental Constraints in Temporary Fresh Waters and 

Their Consequences for the Insect Fauna,” Journal of the North American Benthological Society

15:634-650 (1996); T.W. Hunsinger and M.J. Lannoo, “Notophthalmus viridescens, Eastern 

Newt,” in M.J. Lannoo, ed., Amphibian Declines: The Conservation Status of United States 

Species (Berkeley, CA: University of California Press, 2005), pp. 912-914). Bays typically are in 

close proximity to each other or to streams, and are surrounded by very flat land, which is 

thought to likely result in surface water connections in large rain events. Id. at 5-49. Amphibians 

and reptiles use bays extensively for breeding and rearing young; these animals can disperse 

many meters on the landscape and possibly enter or be food in downstream waters. Similarly, 

bays foster abundant insects that have the ability to become part of the downstream food chain 

for fish. 

Prairie potholes are a complex of glacially-formed wetlands and waterbodies, usually 

occurring in depressions that lack permanent natural outlets, and are located in the north-central 

United States and southern Canada, the area commonly known as the Prairie Pothole Region 

(PPR). Report at 5-58 (citing H.A. Kantrud, et al., Prairie Basin Wetlands of the Dakotas: A 

Community Profile, Biological Report 85(7.28) (Washington, D.C.: U.S. Department of the 

Interior, Fish and Wildlife Service and U.S. Environmental Protection Agency, 1989)). The clay 

that underlies potholes allows for the collection and temporary retention of water. Precipitation 
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in the form of spring snowmelt runoff and/or direct summer rainfall is the primary source of 

water inflows, though some potholes also receive groundwater discharge. Id. at 5-58 (citing T.C. 

Winter and D.O. Rosenberry, “Hydrology of Prairie Pothole Wetlands during Drought and 

Deluge: A 17-year Study of the Cottonwood Lake Wetland Complex in North Dakota in the 

Perspective of Longer Term Measured and Proxy Hydrological Records,” Climatic Change

40:189-209 (1998); R. Carroll, et al., “Simulation of a Semipermanent Wetland Basin in the 

Cottonwood Lake Area, East-Central North Dakota,” Journal of Hydrologic Engineering 10:70-

84 (2005)). Water outflow occurs mostly through evapotranspiration and also through shallow or 

regional groundwater recharge. Id. (citing R. Carroll, et al. 2005; G. van der Kamp and M. 

Hayashi, “Groundwater-Wetland Ecosystem Interaction in the Semiarid Glaciated Plains of 

North America,” Hydrogeology Journal 17:203-214 (2009)). The degree to which potholes are 

connected or have the ability to be connected to downstream waters is dependent on many 

factors such as distance to rivers and streams, topography, precipitation, climate cycles (seasonal 

and on longer time scales), biotic community composition, and man-made drainage. Id. at 5-66. 

Within the PPR, distance to rivers and streams is strongly influenced by the three major 

physiographic regions (Red River Valley, Drift Prairie, and Missouri Coteau), which vary in 

number of potholes and stream density, among other factors with relevance to connectivity. Id. at 

5-59, 5-66. Potholes in the Red River Valley, in particular, because of the wetter climatic 

condition and the predominant soil type, may be a region with strong connectivity to downstream 

waters. Id. at 5-61, 5-62 (citing S.G. Leibowitz, and K.C. Vining, “Temporal connectivity in a 

prairie pothole complex,” Wetlands 23:13-25 (2003)). Hydrologic sink and/or source functions 

of potholes can physically and chemically impact downstream waters in the PPR, including 

multiple aspects of flow and associated transport of nutrients, sediment and pesticides. Id. at 5-
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66. In turn, these features affect river geomorphology and biological communities, thus having 

an impact on physical and biological integrity of downstream waters. Additionally, potholes may 

have direct biological effects on downstream river networks via connectivity of resident 

populations, although these effects are less well-known and studied. Id. Some prairie potholes 

also discharge through overland flow when they have reached their capacity to hold water, often 

spilling over into downstream waters. Id. at 5-62 (citing Winter and Rosenberry 1998; Leibowitz 

and Vining 2003; S.N. Kahara, et al., “Spatiotemporal patterns of wetland occurrence in the 

prairie pothole region of eastern South Dakota,” Wetlands 29:678-689 (2009)).

Vernal pools are typically shallow seasonal wetlands that accumulate water during 

colder, wetter months and gradually dry down during warm, dryer months. Id. at 5-66. Vernal 

pools are generally separated into two categories: western vernal pools (located in coastal areas 

of the Western states) and northern vernal pools (located in glaciated areas of Northeastern and 

Midwestern states), which the case study examines separately. Id. at 5-67 (citing P.H. Zedler, 

“Vernal Pools and the Concept of ‘Isolated Wetlands,’” Wetlands 23:597-607 (2003)). In the 

aquatic phase, some western vernal pools are filled to capacity in most years, creating conditions 

under which water can flow from pools into downstream waters, thus providing a seasonal 

hydrologic connection to downstream waters. Id. at 5-22, 5-70 to 5-71 (citing T. Hanes, and L. 

Stromberg, “Hydrology of vernal pools on non-volcanic soils in the Sacramento Valley,” in

C.W. Witham, et al., ed., Ecology, Conservation, and Management of Vernal Pool Ecosystems –

Proceedings from a 1996 Conference (Sacramento, CA: California Native Plant Society, 1998),

pp. 38-49; C.R. Pyke, “Simulating vernal pool hydrologic regimes for two locations in 

California, USA,” Ecological Modelling 173:109-127 (2004); M.C. Rains, et al., “Geological 

control of physical and chemical hydrology in California vernal pools,” Wetlands 28:347-362 
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(2008)). Indirect evidence indicates that Northern vernal pools without perched aquifers are 

hydrologically connected to downstream waters via surface and sub-surface flows. Id. at 5-71 to 

5-72 (citing R.B. Boone, et al., “Simulating Vernal Pool Hydrology in Central Minnesota, USA,” 

Wetlands 26:581-592 (2006)). Although individually small, temporary storage of heavy rainfall 

and snowmelt in vernal pool systems can attenuate flooding, provide a reservoir for adjacent 

vegetation during the spring growth period, and increase nutrient availability, particularly when 

vernal pools are considered in the aggregate with similarly situated vernal pools. See, e.g., id. at 

5-72 (citing W.A. Hobson and R.A. Dahlgren, “Soil Forming Processes in Vernal Pools of 

Northern California, Chico Area,” in C. W. Witham, et al., ed., Ecology, Conservation, and 

Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference, (Sacramento, 

CA: California Native Plant Society, 1998), pp. 24-37). During the seasonal period of 

inundation, aquatic species depend on vernal pools for completion of their life cycles. Id. at 5-67

(citing P.H. Zedler, “Vernal Pools and the Concept of ‘Isolated Wetlands,’” Wetlands 23:597-

607 (2003)). Many insects and amphibians that can live in streams or more permanent pools 

opportunistically use Northern vernal pools as alternative breeding habitat, refuge from predators 

or environmental stressors, hunting or foraging habitat, or stepping-stone corridors for dispersal 

and migration, providing biological connections between pools and downstream waters. Id. at 5-

73 (citing R.D. Semlitsch and J.R. Bodie, “Are Small, Isolated Wetlands Expendable?,” 

Conservation Biology 12:1129-1133 (1998); R.T. Brooks, “Annual and Seasonal Variation and 

the Effects of Hydroperiod on Benthic Macroinvertebrates of Seasonal Forest (‘Vernal’) Ponds 

in Central Massachusetts, USA,” Wetlands 20:707-715 (2000); J.W. Gibbons, et al., 

“Remarkable Amphibian Biomass and Abundance in an Isolated Wetland: Implications for 

Wetland Conservation,” Conservation Biology 20:1457-1465 (2006)). As stated previously, non-
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glaciated vernal pools in western states are periodically connected downstream and have 

functioned as refuges of plants and animal diversity since the Mesozoic era; they are currently 

reservoirs of biodiversity and are possibly genetically connected to other locations and aquatic 

habitats through continuing dispersal. Id. at 5-72 (citing J.L. King, et al., “Species Richness, 

Endemism and Ecology of Crustacean Assemblages in Northern California Vernal Pools,” 

Hydrobiologia 328:85-116 (1996); E.T. Bauder and S. McMillan, “Current Distribution and 

Historical Extent of Vernal Pools in Southern California and Northern Baja California, Mexico,” 

in C. W. Witham, et al., ed., (1998), pp. 56-70; J.E. Keeley and P.H. Zedler, “Characterization 

and Global Distribution of Vernal Pools,” in C.W. Witham, et al., ed., (1998), pp. 1-14; P.H. 

Zedler, “Vernal Pools and the Concept of ‘Isolated Wetlands,’” Wetlands 23:597-607 (2003)). 

Organisms, including invertebrates and zooplankton may be flushed from Western pools into 

downstream waters (sometimes over long distances) during the seasonal periods of overflow, 

carried by animal vectors (including humans), or dispersed by wind, further supporting a 

biological connection between western pools and downstream waters. Id. at 5-73 (citing B. 

Vanschoenwinkel, et al., “Wind Mediated Dispersal of Freshwater Invertebrates in a Rock Pool 

Metacommunity: Differences in Dispersal Capacities and Modes,” Hydrobiologia 635:363-372 

(2009)). 

The evidence in the literature regarding Carolina and Delmarva bays, prairie potholes, 

and vernal pools is illustrative of the literature regarding “other waters” that are not (a)(1) 

through (a)(6) waters. Scientific literature to date has infrequently had as the main objective of 

the study to evaluate the connectivity to downstream waters, though this is a topic of increasing 

interest to scientists. S.G. Leibowitz and T.-L. Nadeau, “Isolated Wetlands: State-of-the-Science 

and Future Directions,” Wetlands 23:517-531 (2003). Nevertheless, the relevant information in 
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the literature may, at some future date when it is more mature, support the existence or the 

likelihood of the existence of a connection between these aquatic resources and downstream 

waters. See, e.g., id. at 5-57, 6-7 . The agencies do not propose to define any of these waters 

categorically as “waters of the United States” such that a case-specific significant nexus 

determination is not required. The agencies seek comment, data, and information on whether 

there are subcategories of “other waters” or specific combinations of characteristics that are 

“likely, in the majority of cases, to perform important functions for an aquatic ecosystem 

incorporating navigable waters,” and, thus, should be per se jurisdictional. For example, if there 

are additional studies addressing the connectivity of prairie potholes in the Red River Valley, 

including the factors influencing that connectivity and how it is important to particular 

downstream waters, that would be relevant information.

Under today’s proposal, on a case-specific basis, “other waters” that have a significant 

nexus to an (a)(1) through (a)(3) water are waters of the United States under (a)(7). Tthe 

scientific literature and data in the Report and elsewhere support that some “other waters”

(including some of those in the case studies), along with other similarly situated waters in the 

region, do greatly affect the chemical, physical, or biological integrity of (a)(1) through (a)(3) 

waters, and thus would be jurisdictional under (a)(7).

Though much of the literature cited in the Report relates to “other waters” that are 

wetlands, the Report indicates that non-wetland waters that are not (a)(1) through (a)(6) waters 

also can have chemical, physical, or biological connections that significantly impact downstream 

waters. For instance, non-adjacent ponds or lakes that are not part of the tributary network can 

still be connected to downstream waters through chemical, physical, and biological connections. 

Lake storage has been found to attenuate peak streamflows in Minnesota. Id. at 5-25 (citing J. 
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Jacques and D.L. Lorenz, Techniques for Estimating the Magnitude and Frequency of Floods of 

Ungauged Streams in Minnesota, USGS Water-Resources Investigations Report 84-4170 

(Washington, D.C.: U.S. Geological Survey, 1988); D.L. Lorenz, et al., Techniques for 

Estimating the Magnitude and Frequency of Peak Flows on Small Streams in Minnesota Based 

on Data through Water Year 2005, U.S. Geological Survey Scientific Investigations Report 

2009-5250 (Reston, VA: U.S. Geological Survey, 2010)). Similar to wetlands, ponds are often 

used by invertebrate, reptile, and amphibian species that also utilized downstream waters for 

various life history requirements, particularly because many ponds, particularly temporary 

ponds, are free of predators, such as fish, that prey on larvae. The American toad and Eastern 

newt are widespread habitat generalists that can move among streams, wetlands, and ponds to 

take advantage of each aquatic habitat, feeding on aquatic invertebrate prey, and avoiding 

predators. See, e.g., Id. at 5-33 (citing K.J. Babbitt et al., “Patterns of Larval Amphibian 

Distribution along a Wetland Hydroperiod Gradient,” Canadian Journal of Zoology-Revue 

Canadienne De Zoologie 81:1539-1552 (2003); D.M. Green, “Bufo americanus, American 

Toad,” in M. Lannoo, ed., Amphibian Declines: The Conservation Status of United States 

Species, (Berkeley, CA: University of California Press, 2005), pp. 692-704; T.W. Hunsinger and 

M.J. Lannoo, “Notophthalmus viridescens, Eastern Newt,” in M. Lannoo, ed., Amphibian 

Declines: The Conservation Status of United States Species, (Berkeley, CA: University of 

California Press, 2005), pp. 912-914; J.W. Petranka and C.T. Holbrook, “Wetland Restoration 

for Amphibians: Should Local Sites Be Designed to Support Metapopulations or Patchy 

Populations?,” Restoration Ecology 14:404-411 (2006)). Additionally, stream networks that are 

not part of the tributary system (e.g., streams in closed basins without an (a)(1) to (a)(3) water or 

losing streams and other streams that cease to flow before reaching downstream (a)(1) to (a)(3) 
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waters) may likewise have a significant impact on the chemical, physical, or biological integrity 

of downstream waters. Non-tributary streams may be connected via groundwater to downstream 

waters. Such streams may also provide habitat to insect, amphibian, and reptile species that also 

use the tributary network. 
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Appendix B

Legal Analysis

Background

Congress enacted the Federal Water Pollution Control Act Amendments of 1972, Pub. L. 

No. 92-500, 86 Stat. 816, as amended, Pub. L. No. 95-217, 91 Stat. 1566 (33 U.S.C. 1251 et seq.) 

(Clean Water Act or CWA) "to restore and maintain the chemical, physical, and biological 

integrity of the Nation's waters." 33 U.S.C. 1251(a).2 The U.S. Supreme Court first addressed the 

scope of waters of the United States protected by the CWA in United States v. Riverside Bayview 

Homes, 474 U.S. 121 (1985), which involved wetlands adjacent to a traditional navigable water 

in Michigan. In a unanimous opinion, the Court deferred to the Corps’ ecological judgment that 

adjacent wetlands are “inseparably bound up” with the waters to which they are adjacent, and 

upheld the inclusion of adjacent wetlands in the regulatory definition of “waters of the United 

States.” Id. at 134. The Court observed that the broad objective of the CWA to restore and 

maintain the integrity of the Nation’s waters “... incorporated a broad, systemic view of the goal 

of maintaining and improving water quality .... Protection of aquatic ecosystems, Congress 

recognized, demanded broad federal authority to control pollution, for ‘[w]ater moves in 

hydrologic cycles and it is essential that discharge of pollutants be controlled at the source.’ In 

keeping with these views, Congress chose to define the waters covered by the Act broadly.” Id.

at 132-33.

The issue of “waters of the United States” was addressed again by the Supreme Court in 

Solid Waste Agency of Northern Cook County (SWANCC) v. U.S. Army Corps of Engineers, 531 

 2 The 1972 legislation extensively amended the Federal Water Pollution Control Act (FWPCA), 

which was originally enacted in 1948. Further amendments to the FWPCA enacted in 1977 

changed the popular name of the statute to the Clean Water Act. See Pub. L. No. 95-217, 91 Stat. 

1566; 33 U.S.C. 1251 note. 
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U.S. 159 (2001). In SWANCC, the Court addressed the question of CWA jurisdiction over 

isolated intrastate ponds that had formed on a proposed solid waste balefill site in Illinois. In 

1986, the Corps explained in preamble language that the agencies interpreted the CWA to protect 

intrastate waters: (a) which are or would be used as habitat by birds protected by Migratory Bird 

Treaties; or (b) which are or would be used as habitat by other migratory birds which cross state 

lines; or (c) which are or would be used as habitat for endangered species; or (d) are used to 

irrigate crops sold in interstate commerce. 51 Fed. Reg. 41, 217 (1986). This interpretation 

came to be known as the “Migratory Bird Rule.” The Corps of Engineers had asserted 

jurisdiction over the ponds as “other waters” under 33 C.F.R. § 328.3(a)(3) based solely on the 

presence of migratory birds. In a 5-4 opinion, the Court held that “33 C.F.R. Section 328.3(a)(3) 

as clarified and applied to petitioner’s balefill site pursuant to the ‘Migratory Bird Rule’ ... 

exceeds the authority granted to [the Corps] under 404 of the CWA.” SWANCC at 174. The 

SWANCC Court noted that in Riverside it had “found that Congress’ concern for the protection 

of water quality and aquatic ecosystems indicated its intent to regulate wetlands ‘inseparably 

bound up’ with the ‘waters of the United States’” and that “it was the significant nexus between 

the wetlands and ‘navigable waters’ that informed our reading of the CWA” in that case. Id. at 

172. SWANCC did not invalidate (a)(3) or other parts of the regulatory definition of “waters of 

the United States.” 

Five years after SWANCC, the U.S. Supreme Court addressed the scope of CWA

protection for wetlands adjacent to tributaries of traditional navigable waters. Rapanos v. United 

States, 547 U.S. 715 (2006). In June 2006, the Justices issued five opinions with no single 

opinion commanding a majority of the Court. The plurality opinion, authored by Justice Scalia, 

stated that “waters of the United States” extended beyond traditional navigable waters to include 
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“relatively permanent, standing or flowing bodies of water.” Id. at 739. Justice Scalia indicated 

that the phrase “relatively permanent” includes “seasonal rivers” but not “streams whose flow is 

‘coming and going at intervals ... broken, fitful ... or existing only, or no longer than, a day.” 

Id. at 732 n. 5. The plurality also concluded that only wetlands with a continuous surface 

connection to other jurisdictional waters are protected by the CWA. Justice Kennedy’s 

concurring opinion took a different approach than Justice Scalia’s. Justice Kennedy concluded 

that “waters of the United States” includes waters “that possess a ‘significant nexus’ to waters 

that are or were navigable in fact or that could reasonably be so made.” Id. at 759. He concluded 

that wetlands have the requisite significant nexus where they “either alone or in combination 

with similarly situated lands in the region, significantly affect the chemical, physical, and 

biological integrity of other covered waters more readily understood as ‘navigable.’” Id. at 780. 

Kennedy’s opinion notes that such a relationship with navigable waters must be more than 

“speculative or insubstantial.” Id. at 780. Neither the plurality nor Kennedy opinion invalidated 

any of the regulatory provisions defining “waters of the United States.”

The Circuit Courts of Appeal are not uniform as to the controlling test for “waters of the 

United States” under Rapanos. The First,Third and Eighth Circuits have concluded that CWA 

jurisdiction exists if either Justice Kennedy’s or the plurality’s standard is met. United States v. 

Johnson, 467 F.3d 56, 66 (1st Cir. 2006), petition for certiorari denied Oct. 9, 2007; U.S. v. 

Donovan,661 F.3d. 174 (3rd Cir. 2012); U.S. v. Bailey, 571 F.3d 791, 798-99 (8th Cir. 2009). The 

Seventh and Ninth Circuits limited their holdings that the Kennedy standard applied to the facts 

of the cases before them, and did not foreclose the possibility that in some cases the plurality’s 

standard might apply. N. Cal. River Watch v. City of Healdsburg, 496 F.3d 993, 999-1000 (9th

Cir. 2007), petition for certiorari denied Feb. 19, 2008; United States v. Gerke Excavating, Inc., 
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464 F.3d 723, 725 (7th Cir. 2006), petition for certiorari denied Oct. 1, 2007. The Fifth and Sixth 

Circuits did not choose a controlling standard because the waters at issue satisfied both 

standards. United States v. Robert J. Lucas, Jr., 516 F.3d 316, 326-27 (5th Cir. 2008), petition 

for certiorari denied Oct. 15, 2008; United States v. Cundiff, 555 F.3d 200, 210-13 (6th Cir. 

2009), petition for certiorari denied Oct. 5, 2009. The Eleventh Circuit has held that only the 

Kennedy standard determines jurisdiction. United States v. McWane, 505 F.3d 1208 (11th Cir. 

2007), petition for certiorari denied Dec. 1, 2008. No Circuit Court has held that only the 

plurality standard applies.

Traditional Navigable Waters:

EPA and the Corps are proposing no changes to the existing regulation at paragraph 

(a)(1) and will continue to assert jurisdiction over “[a]ll waters which are currently used, or were 

used in the past, or may be susceptible to use in interstate or foreign commerce, including all 

waters which are subject to the ebb and flow of the tide.” 33 C.F.R. § 328.3(a)(1); 40 C.F.R. § 

230.3(s)(1); 40 C.F.R. § 122.2 (“waters of the U.S.”(a)); 40 C.F.R. § 110.1(a) (“navigable 

waters”). These “(a)(1)waters” are the “traditional navigable waters.” These (a)(1) waters 

include all of the “navigable waters of the United States,” defined in 33 C.F.R. Part 329 and by 

numerous decisions of the federal courts, plus all other waters that are navigable-in-fact (e.g., the 

Great Salt Lake, UT and Lake Minnetonka, MN).

To determine whether a water body constitutes an (a)(1) water under the regulations, 

relevant considerations include Corps regulations, prior determinations by the Corps and by the 

federal courts, and case law. Corps districts and EPA regions would determine whether a 

particular waterbody is a traditional navigable water based on application of those considerations 
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to the specific facts in each case.

As noted above, the (a)(1) waters include, but are not limited to, the “navigable waters of 

the United States.” A water body qualifies as a “navigable water of the United States” if it meets 

any of the tests set forth in 33 C.F.R. Part 329 (e.g., the water body is (a) subject to the ebb and 

flow of the tide, and/or (b) the water body is presently used, or has been used in the past, or may 

be susceptible for use (with or without reasonable improvements) to transport interstate or 

foreign commerce). The Corps districts have made determinations in the past regarding whether 

particular water bodies qualify as “navigable waters of the United States” for purposes of 

asserting jurisdiction under Sections 9 and 10 of the Rivers and Harbors Act of 1899 (33 USC 

Sections 401 and 403). Pursuant to 33 C.F.R. § 329.16, the Corps maintains lists of final 

determinations of navigability for purposes of Corps jurisdiction under the Rivers and Harbors 

Act of 1899. While absence from the list should not be taken as an indication that the water is not 

navigable (329.16(b)), Corps districts and EPA regions rely on any final Corps determination 

that a water body is a navigable water of the United States.

If the federal courts have determined that a water body is navigable-in-fact under federal 

law for any purpose, that water body qualifies as a “traditional navigable water” subject to CWA 

jurisdiction under 33 C.F.R. § 328.3(a)(1) and 40 C.F.R. § 230.3(s)(1). Corps districts and EPA 

regions are guided by the relevant opinions of the federal courts in determining whether 

waterbodies are “currently used, or were used in the past, or may be susceptible to use in 

interstate or foreign commerce” (33 C.F.R. § 328.3(a)(1); 40 C.F.R. § 230.3(s)(1)) or “navigablein-fact.”

This definition of “navigable-in-fact” comes from a long line of cases originating with 

The Daniel Ball, 77 U.S. 557 (1870). The Supreme Court stated:
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Those rivers must be regarded as public navigable rivers in law which are 

navigable in fact. And they are navigable in fact when they are used, or are 

susceptible of being used, in their ordinary condition, as highways for commerce, 

over which trade and travel are or may be conducted in the customary modes of 

trade and travel on water.

The Daniel Ball, 77 U.S. at 563.

In The Montello, the Supreme Court clarified that “customary modes of trade and travel 

on water” encompasses more than just navigation by larger vessels:

The capability of use by the public for purposes of transportation and commerce 

affords the true criterion of the navigability of a river, rather than the extent and 

manner of that use. If it be capable in its natural state of being used for purposes 

of commerce, no matter in what mode the commerce may be conducted, it is 

navigable in fact, and becomes in law a public river or highway.

The Montello, 87 U.S. 430, 441-42 (1874). In that case, the Court held that early fur trading 

using canoes sufficiently showed that the Fox River was a navigable water of the United States. 

The Court was careful to note that the bare fact of a water’s capacity for navigation alone is not 

sufficient; that capacity must be indicative of the water’s being “generally and commonly useful 

to some purpose of trade or agriculture.” Id. at 442.

In Economy Light & Power, the Supreme Court held that a waterway need not be 

continuously navigable; it is navigable even if it has “occasional natural obstructions or 

portages” and even if it is not navigable “at all seasons . . . or at all stages of the water.” 

Economy Light & Power Co. v. U.S., 256 U.S. 113, 122 (1921).

In United States v. Holt State Bank, 270 U.S. 49 (1926), the Supreme Court summarized 
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the law on navigability as of 1926 as follows:

The rule long since approved by this court in applying the Constitution and laws 

of the United States is that streams or lakes which are navigable in fact must be 

regarded as navigable in law; that they are navigable in fact when they are used, 

or are susceptible of being used, in their natural and ordinary condition, as 

highways for commerce, over which trade and travel are or may be conducted in 

the customary modes of trade and travel on water; and further that navigability 

does not depend on the particular mode in which such use is or may be had -

whether by steamboats, sailing vessels or flatboats- nor on an absence of 

occasional difficulties in navigation, but on the fact, if it be a fact, that the stream 

in its natural and ordinary condition affords a channel for useful commerce.

Holt State Bank, 270 U.S. at 56.

In U. S. v. Utah, 283 U.S. 64 (1931) and U.S. v. Appalachian Elec. Power Co, 311 U.S. 

377 (1940), the Supreme Court held that so long as a water is susceptible to use as a highway of 

commerce, it is navigable-in-fact, even if the water has never been used for any commercial 

purpose. U.S. v. Utah, at 81-83 (“The question of that susceptibility in the ordinary condition of 

the rivers, rather than of the mere manner or extent of actual use, is the crucial question.”); U.S. 

v. Appalachian Elec. Power Co., 311 U.S. 377, 416 (1940) (“Nor is lack of commercial traffic a 

bar to a conclusion of navigability where personal or private use by boats demonstrates the 

availability of the stream for the simpler types of commercial navigation.”).

In 1971, in Utah v. United States, 403 U.S. 9 (1971), the Supreme Court held that the 

Great Salt Lake, an intrastate water body, was navigable under federal law even though it “is not 

part of a navigable interstate or international commercial highway.” Id. at 10. In doing so, the 
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Supreme Court stated that the fact that the Lake was used for hauling of animals by ranchers 

rather than for the transportation of “water-borne freight” was an “irrelevant detail.” Id. at 11. 

“The lake was used as a highway and that is the gist of the federal test.” Id.

Also of note are two decisions from the courts of appeals. In FPL Energy Marine Hydro, 

a case involving the Federal Power Act, the D.C. Circuit reiterated the fact that “actual use is not 

necessary for a navigability determination” and repeated earlier Supreme Court holdings that 

navigability and capacity of a water to carry commerce could be shown through “physical 

characteristics and experimentation.” FPL Energy Marine Hydro LLC v. FERC, 287 F.3d 1151, 

1157 (D.C. Cir. 2002). In that case, the D.C. Circuit upheld a FERC navigability determination 

that was based upon three experimental canoe trips taken specifically to demonstrate the river’s 

navigability. Id. at 1158-59.

The 9th Circuit has also implemented the Supreme Court’s holding that a water need only 

be susceptible to being used for waterborne commerce to be navigable-in-fact. Alaska v. Ahtna, 

Inc., 891 F.2d 1404 (9th Cir. 1989). In Ahtna, the 9th Circuit held that current use of an Alaskan 

river for commercial recreational boating is sufficient evidence of the water’s capacity to carry 

waterborne commerce at the time that Alaska became a state. Id. at 1405. It was found to be 

irrelevant whether or not the river was actually being navigated or being used for commerce at 

the time, because current navigation showed that the river always had the capacity to support 

such navigation. Id. at 1404.

In summary, when determining whether a water body qualifies as a “traditional navigable 

water” (i.e., an (a)(1) water), relevant considerations include whether a Corps District has 

determined that the water body is a navigable water of the United States pursuant to 33 C.F.R § 

329.14, or the water body qualifies as a navigable water of the United States under any of the 
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tests set forth in 33 C.F.R. § 329, or a federal court has determined that the water body is 

navigable-in-fact under federal law for any purpose, or the water body is “navigable-in-fact” 

under the standards that have been used by the federal courts.

Interstate Waters:

1. Interstate Waters

The agencies’ proposal today makes no change to the interstate waters section of the 

existing regulations and the agencies would continue to assert jurisdiction over interstate waters, 

including interstate wetlands. The language of the CWA is clear that Congress intended the term 

“navigable waters” to include interstate waters, and the agencies’ interpretation, promulgated 

contemporaneously with the passage of the CWA, is consistent with the statute and legislative 

history. The Supreme Court’s decisions in SWANCC and Rapanos did not address the interstate 

waters provision of the existing regulation.

A. The Language of the Clean Water Act, the Statute as a Whole, and the 

Statutory History Demonstrate Congress’ Clear Intent to Include Interstate 

Waters as “Navigable Waters” Subject to the Clean Water Act

While as a general matter, the scope of the terms “navigable waters” and “waters of the 

United States” is ambiguous, the language of the CWA, particularly when read as a whole, 

demonstrates that Congress clearly intended to continue to subject interstate waters to federal 

regulation. The statutory history of federal water pollution control places the terms of the CWA 

in context and provides further evidence of Congressional intent to include interstate waters 

within the scope of the “navigable waters” protected by the Act. Congress clearly intended to 

subject interstate waters to CWA jurisdiction without imposing a requirement that they be water 
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that is navigable for purposes of federal regulation under the Commerce Clauses themselves or 

be connected to water that is navigable for purposes of federal regulation under the Commerce 

Clauses.3 The CWA itself is clear that interstate waters that were previously subject to federal 

regulation remain subject to federal regulation. The text of the CWA, specifically the CWA’s 

provision with respect to interstate waters and their water quality standards, in conjunction with 

the definition of navigable waters, provides clear indication of Congress’ intent. Thus, interstate 

waters are “navigable waters” protected by the CWA.

(1) The Plain Language of the Clean Water Act and the Statute as a Whole 

Clearly Indicate Congress’ Intent to Include Interstate Waters within the Scope of 

“Navigable Waters” for Purposes of the Clean Water Act

Under well settled principles, the phrase “navigable waters” should not be read in 

isolation from the remainder of the statute. As the Supreme Court has explained:

The definition of words in isolation, however, is not necessarily controlling in 

statutory construction. A word in a statute may or may not extend to the outer 

limits of its definitional possibilities. Interpretation of a word or phrase depends 

upon reading the whole statutory text, considering the purpose and context of the 

statute, and consulting any precedents or authorities that inform the analysis.

Dolan v. U.S. Postal Service, 546 U.S. 481, 486 (2006); see also United States Nat’l. Bank of 

Oregon v. Indep. Ins. Agents of Am., Inc., 508 U.S. 439, 455 (1993).

 3 For purposes of the CWA, EPA and the Corps have interpreted the term “traditional navigable waters” to include 

all of the “navigable waters of the United States,” defined in 33 C.F.R. Part 329 and by numerous decisions of the 

federal courts, plus all other waters that are navigable-in-fact (e.g., the Great Salt Lake, UT and Lake Minnetonka 

MN). This section explains why EPA and the Corps do not interpret the CWA or the Supreme Court’s decisions in 

Solid Waste Agency of Northern Cook County (SWANCC) v. U.S. Army Corps of Engineers, 531 U.S. 159 (2001) 

and Rapanos v. United States, 547 U.S. 715 (2006), to restrict CWA jurisdiction over interstate waters to only those 

interstate waters that are traditional navigable waters or that connect to traditional navigable waters.
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While the term “navigable waters” is, in general, ambiguous, interstate waters are waters 

that are clearly covered by the plain language of the definition of “navigable waters.”4 Congress 

defined “navigable waters” to mean “the waters of the United States, including the territorial 

seas.” Interstate waters are the waters of the several States and, thus, the United States. While 

the 1972 Act was clearly not limited to interstate waters, it was clearly intended to include 

interstate waters.

Furthermore, the CWA does not simply define “navigable waters.” Other provisions of 

the statute provide additional textual evidence of the scope of the primary jurisdictional term of 

the Act. Most importantly, there is a specific provision in the 1972 CWA establishing 

requirements for those interstate waters which were subject to the prior Water Pollution Control 

acts. 

The CWA requires States to establish water quality standards for navigable waters and 

submit them to the Administrator for review.5 Under section 303(a) of the Act:

In order to carry out the purpose of this Act, any water quality standard applicable 

to interstate waters which was adopted by any State and submitted to, and 

approved by, or is awaiting approval by, the Administrator pursuant to this Act as 

in effect immediately prior to the date of enactment of the Federal Water 

Pollution Control Act Amendments of 1972, shall remain in effect unless the 

Administrator determined that such standard is not consistent with the applicable 

 4 The Supreme Court has found that the term “waters of the United States” is ambiguous in some respects. 

Rapanos, 547 U.S. at 752 (plurality opinion), 804 (dissent).

5

 Section 303 of the Act requires the States to submit revised and new water quality standards to the Administrator 

for review. CWA section 303(c)(2)(A). Such revised or new water quality standards “shall consist of the 

designated uses of the navigable waters involved and the water quality criteria for such waters.” Id. If the 

Administrator determines that a revised or new standard is not consistent with the Act’s requirements, or determines 

that a revised or new standard is necessary to meet the Act’s requirements, and the State does not make required 

changes, “[t]he Administrator shall promptly prepare and publish proposed regulations setting forth a revised or new 

water quality standard for the navigable waters involved.” CWA section 303(c)(4).
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requirements of this Act as in effect immediately prior to the date of enactment of 

the Federal Water Pollution Control Act Amendments of 1972. If the 

Administrator makes such a determination he shall, within three months after the 

date of enactment of the Federal Water Pollution Control Act Amendments of 

1972, notify the State and specify the changes needed to meet such requirements. 

If such changes are not adopted by the State within ninety days after the date of 

such notification, the Administrator shall promulgate such changes in accordance 

with subsection (b) of this section.

CWA section 303(a)(1) (emphasis added).

Under the 1965 Act, as discussed in more detail below, States were directed to develop 

water quality standards establishing water quality goals for interstate waters. By the early 1970s, 

all the States had adopted such water quality standards. Advanced Notice of Proposed 

Rulemaking, Water Quality Standards Regulation, 63 Fed. Reg. 36742, 36745 (July 7, 1998). In 

section 303(a), Congress clearly intended for existing federal regulation of interstate waters to 

continue under the amended CWA. Water quality standards for interstate waters were not 

merely to remain in effect, but EPA was required to actively assess those water quality standards 

and even promulgate revised standards for interstate waters if States did not make necessary 

changes. By the plain language of the statute, these water quality standards for interstate waters 

were to remain in effect “in order to carry out the purpose of this Act.” The objective of the Act 

is “to restore and maintain the chemical, physical, and biological integrity of the Nation’s 

waters.” CWA section 101(a). It would contravene Congress’ clearly stated intent for a court to 

impose an additional jurisdictional requirement on all rivers, lakes, and other waters that flow 

across, or form a part of, State boundaries (“interstate waters” as defined by the 1948 Act, § 10, 
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62 Stat. 1161), such that interstate waters that were previously protected were no longer 

protected because they lacked a connection to a water that is navigable for purposes of federal 

regulation under the Commerce Clause. Nor would the existing water quality standards be 

“carry[ing] out the purpose of this Act,” if only those water quality standards established for 

interstate waters that are also water that is navigable for purposes of federal regulation under the 

Commerce Clauses or that connect to water that is navigable for purposes of federal regulation 

under the Commerce Clauses could be implemented under the Act through, for example, 

National Pollutant Discharge Elimination System permits under Section 402 of the Act. 

Nowhere in Section 303(a) does Congress make such a distinction.

(2) The Federal Water Pollution Control Statute That Became the Clean Water Act 

Covered Interstate Waters 

In 1972, when Congress rewrote the law governing water pollution, two federal statutes 

addressed discharges of pollutants into interstate waters and water that is navigable for purposes 

of federal regulation under the Commerce Clause, and tributaries of each: the Water Pollution 

Control Act of 1948, as amended, and Section 13 of the Rivers and Harbors Act of 1899 (known 

as the “Refuse Act”). Of the two, the Water Pollution Control Act extended federal authority 

over interstate waters and their tributaries. In contrast, the Refuse Act extended federal 

jurisdiction over the “navigable waters of the United States” and their tributaries. These two 

separate statutes demonstrate that Congress recognized that interstate waters and “navigable 

waters of the United States” were independent lawful bases of federal jurisdiction. 

a. The Federal Water Pollution Control Act Prior to 1972

 From the outset, and through all the amendments pre-dating the 1972 Amendments, the 

federal authority to abate water pollution under the Water Pollution Control Act, and the Federal 
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Water Pollution Control Act (FWPCA) as it was renamed in 1956, extended to interstate waters. 

In addition, since first enacted in 1948, and throughout all the amendments, the goals of the Act 

have been, inter alia, to protect public water supplies, propagation of fish and aquatic life, 

recreation, agricultural, industrial, and other legitimate uses. See 62 Stat. 1155 and 33 U.S.C. § 

466 (1952), 33 U.S.C. § 466 (1958), 33 U.S.C. § 466 (1964), 33 U.S.C. § 1151 (1970).

In 1948, Congress enacted the Water Pollution Control Act “in connection with the 

exercise of jurisdiction over the waterways of the Nation and in the consequence of the benefits 

to public health and welfare by the abatement of stream pollution.” See Pub. L. No. 80-845, 62 

Stat. 1155 (June 30, 1948). The Act authorized technical assistance and financial aid to States 

for stream pollution abatement programs, and made discharges of pollutants into interstate 

waters and their tributaries a nuisance, subject to abatement and prosecution by the United 

States. See § 2(d)(1),(4), 62 Stat. at 1156-1157 (Section 2(d)(1) of the Water Pollution Control

Act of 1948, 62 Stat. at 1156, stated: “The pollution of interstate waters in or adjacent to any 

State or States (whether the matter causing or contributing to such pollution is discharged 

directly into such waters or reaches such waters after discharge into a tributary of such waters), 

which endangers the health or welfare of persons in a State other than that in which the discharge 

originates, is hereby declared to be a public nuisance and subject to abatement as herein 

provided.” (emphasis added)); § 2(a), 62 Stat. 1155 (requiring comprehensive programs for 

“interstate waters and tributaries thereof”); § 5, 62 Stat. 1158 (authorizing loans for sewage 

treatment to abate discharges into “interstate waters or into a tributary of such waters”). Under 

the statute, “interstate waters” were defined as all rivers, lakes, and other waters that flow across, 

or form a part of, State boundaries. § 10, 62 Stat. 1161. 
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In 1956, Congress strengthened measures for controlling pollution of interstate waters 

and their tributaries. Pub. L. No. 84-660, 70 Stat. 498 (1956) (directing further cooperation 

between the federal and State governments in development of “comprehensive programs for 

eliminating or reducing the pollution of interstate waters and tributaries . . . and improving the 

sanitary condition of surface and underground waters,” and authorizing the Surgeon General to 

make joint investigations with States into the conditions of and discharges into “any waters of 

any State or States.”).

In 1961, Congress amended the FWPCA to substitute the term “interstate or navigable 

waters” for “interstate waters.” See Pub. L. No. 87-88, 75 Stat. 208 (1961). Accordingly, 

beginning in 1961, the provisions of the FWPCA applied to all interstate waters and navigable 

waters and the tributaries of each, see 33 U.S.C. §§ 466a, 466g(a) (1964).6

 

In 1965, Congress approved a second set of major legislative changes, requiring each 

State to develop water quality standards for interstate waters within its boundaries by 1967. Pub. 

L. No. 89-234, 79 Stat. 908 (1965).7

 Failing establishment of adequate standards by the State, 

the Act authorized establishment of water quality standards by federal regulation. Id. at 908. 

The 1965 Amendments provided that the “discharge of matter into such interstate waters or 

portions thereof, which reduces the quality of such waters below the water quality standards 

established under this subsection (whether the matter causing or contributing to such reduction is 

discharged directly into such waters or reaches such waters after discharge into tributaries of 

 6

 Congress did not define the term “navigable waters” in the 1961 Amendments, or in subsequent FWPCA 

Amendments, until 1972.

 

7

 In 1967, the State of Arizona created the Water Quality Control Council (Council) to implement the requirements 

of the 1965 FWPCA. The Council adopted water quality standards for those waters that were considered “interstate 

waters” pursuant to the existing federal law. The Council identified the Santa Cruz River as an interstate water and 

promulgated water quality standards for the river in accordance with federal law.
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such waters), is subject to abatement” through procedures specified in the Act, including (after 

conferences and negotiations and consideration by a Hearing Board) legal action in the courts. 

Id. at 909.8 

b. The Refuse Act 

Since its original enactment in 1899, the Refuse Act has prohibited the discharge of 

refuse matter “into any navigable water of the United States, or into any tributary of any 

navigable water.” Ch. 425, 30 Stat. 1152 (1899). It also has prohibited the discharge of such 

material on the bank of any tributary where it is liable to be washed into a navigable water. Id. 

Violators are subject to fines and imprisonment. Id. at 1153 (codified at 33 U.S.C. § 412). In 

1966, the Supreme Court upheld the Corps’ interpretation of the Refuse Act as prohibiting 

discharges that pollute the navigable waters, and not just those discharges that obstruct 

navigation. United States v. Standard Oil Co., 384 U.S. 224, 230 (1966). In 1970, President 

Nixon signed an Executive Order directing the Corps (in consultation with the Federal Water 

Pollution Control Administration9

) to implement a permit program under Section 13 of the RHA 

“to regulate the discharge of pollutants and other refuse matter into the navigable waters of the 

United States or their tributaries and the placing of such matter upon their banks.” E.O. 11574, 

35 Fed. Reg. 19,627 (Dec. 25, 1970). In 1971, the Corps promulgated regulations establishing 

the Refuse Act Permit Program. 36 Fed. Reg. 6564, 6565 (April 7, 1971). The regulations made 

it unlawful to discharge any pollutant (except those flowing from streets and sewers in a liquid 

state) “into a navigable waterway or tributary,” except pursuant to a permit. Under the permit 

 8

 The 1966 Amendments authorized civil fines for failing to provide information about an alleged discharge causing 

or contributing to water pollution. Pub. L. No. 89-753, 80 Stat. 1250 (1966); see also S. Rep. No. 414, 92d 

Congress, 1st Sess. 10 (1972) (describing the history of the FWPCA).

9

 In December 1970, administration of the Federal Water Pollution Control Administration was transferred from the 

Secretary of the Interior to EPA. S. Rep. No. 414, 92d Congress, 1st Sess. (1972). 
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program, EPA advised the Corps regarding the consistency of a proposed discharge with water 

quality standards and considerations, and the Corps evaluated a permit application for impacts on 

anchorage, navigation, and fish and wildlife resources. Id. at 6566. 

c. The Federal Water Pollution Control Act of 1972

When Congress passed the Federal Water Pollution Control Act amendments of 1972 

(referred to hereinafter as the CWA or CWA), it was not acting on a blank slate. It was 

amending existing law that provided for a federal/state program to address water pollution. The 

Supreme Court has recognized that Congress, in enacting the CWA in 1972, “intended to 

repudiate limits that had been placed on federal regulation by earlier water pollution control 

statutes and to exercise its powers under the Commerce Clause to regulate at least some waters 

that would not be deemed ‘navigable’ under the classical understanding of that term.” Riverside 

Bayview Homes, 474 U.S. at 133; see also International Paper Co. v. Ouellette, 479 U.S. 481, 

486, n.6 (1987). 

The amendments of 1972 defined the term “navigable waters” to mean “the waters of the 

United States, including the territorial seas.” 33 U.S.C. § 1362(7). While earlier versions of the 

1972 legislation defined the term to mean “the navigable waters of the United States,” the 

Conference Committee deleted the word “navigable” and expressed the intent to reject prior 

geographic limits on the scope of federal water-protection measures. Compare S. Conf. Rep. No. 

1236, 92d Cong., 2d Sess. 144 (1972), with H.R. Rep. No. 911, 92 Cong., 2d Sess. 356 (1972) 

(bill reported by the House Committee provided that “[t]he term ‘navigable waters’ means the 

navigable waters of the United States, including the territorial seas”); see also S. Rep. No. 414, 

92d Cong., 1st Sess. 77 (“Through a narrow interpretation of the definition of interstate waters 

the implementation of the 1965 Act was severely limited. . . . Therefore, reference to the control 
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requirements must be made to the navigable waters, portions thereof, and their tributaries.”). 

Thus, Congress intended the scope of the 1972 Act to include, at a minimum, the waters already 

subject to federal water pollution control law – both interstate waters and water that is navigable 

for purposes of federal regulation under the Commerce Clause. Those statutes covered interstate 

waters, defined interstate waters without requiring that they be a traditional navigable water or be 

connected to water that is a traditional navigable water, and demonstrated that Congress knew 

that there are interstate waters that are not navigable for purposes of federal regulation under the 

Commerce Clause. 

In fact, Congress amended the Water Pollution Control Act in 1961 to substitute the term 

“interstate or navigable waters” for “interstate waters,” demonstrating that Congress wanted to 

be very clear that it was asserting jurisdiction over both types of waters: interstate waters even if 

they were not navigable for purposes of federal regulation under the Commerce Clause, and 

traditional navigable waters even if they were not interstate waters. At no point were the 

interstate waters already subject to federal water pollution control authority required to be 

navigable or to connect to a traditional navigable water. Further, as discussed above, the 

legislative history clearly demonstrates that Congress was expanding jurisdiction – not 

narrowing it – with the 1972 amendments. Thus, it is reasonable to conclude that by defining 

“navigable waters” as “the waters of the United States” in the 1972 amendments, Congress 

included not just traditionally navigable waters, but all waters previously regulated under the 

FWPCA, including non-navigable interstate waters.

Based on the statutory definition of navigable waters, the requirement of Section 303(a) 

for water quality standards for interstate waters to remain in effect, the purposes of the Act, and 

the more than three decades of federal water pollution control regulation that provides a context 
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for reading those provisions of the statute, the intent of Congress is clear that the term “navigable 

waters” includes “interstate waters” as an independent basis for CWA jurisdiction, whether or 

not they themselves are traditional navigable waters or are connected to a traditional navigable 

water.

B. Supreme Court Precedent Supports CWA Jurisdiction Over Interstate 

Waters Without Respect to Navigability

In two seminal decisions, the Supreme Court established that resolving interstate water 

pollution issues was a matter of federal law and that the CWA was the comprehensive regulatory 

scheme for addressing interstate water pollution. Illinois v. Milwaukee, 406 U.S. 91 (1972); City 

of Milwaukee v. Illinois, 451 U.S. 304 (1981). In both of these decisions, the Court held that 

federal law applied to interstate waters. Moreover, these cases analyzed the applicable federal 

statutory schemes and determined that the provisions of the Federal Water Pollution Control Act 

and the CWA regulating water pollution applied generally to interstate waters. The holdings of 

these cases recognized the federal interest in interstate water quality pollution; and City of 

Milwaukee recognized that CWA jurisdiction extends to interstate waters without regard to 

navigability.

In Illinois v. Milwaukee, the Court considered a public nuisance claim brought by the 

State of Illinois against the City of Milwaukee to address the adverse effects of Milwaukee’s 

discharges of poorly treated sewage into Lake Michigan, “a body of interstate water.” 406 U.S. 

at 93. In relevant part, the Court held that the federal common law of nuisance was an 

appropriate mechanism to resolve disputes involving interstate water pollution. 406 U.S. at 107 

(“federal courts will be empowered to appraise the equities of suits alleging creation of a public 

nuisance by water pollution”). The Court further noted that in such actions the Court could 
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consider a State’s interest in protecting its high water quality standards from “the more degrading 

standards of a neighbor.” Id.

In reaching this conclusion, the Court examined in detail the scope of the federal 

regulatory scheme as it existed prior to the October, 1972 FWPCA amendments. In its April, 

1972 decision, the Court concluded that the Federal Water Pollution Control Act “makes clear 

that it is federal, not state, law that in the end controls the pollution of interstate or navigable 

waters.” 406 U.S. at 102 (emphasis added). The Court, in this case, concluded that the 

regulatory provisions of the Federal Water Pollution Control Act did not address the right of a 

state to file suit to protect water quality. However, this was not because this statute did not reach 

interstate waters. The Court specifically noted that Section 10(a) of the Federal Water Pollution 

Control Act “makes pollution of interstate or navigable waters subject ‘to abatement’” 406 U.S. 

at 102 (emphasis added). Rather, the Court noted that the plaintiff in this action was seeking 

relief outside the scope of the Federal Water Pollution Control Act and that statute explicitly 

provided that independent “‘state and interstate action to abate pollution of interstate or 

navigable waters shall be encouraged and shall not ... be displaced by Federal enforcement 

action.” 406 U.S. at 104 (citing section 10(b) of the Federal Water Pollution Control Act).

In addition, in Illinois v. Milwaukee, the Court acknowledged that it was essential for 

federal law to resolve interstate water pollution disputes, citing with approval the following 

discussion from Texas v. Pankey:

Federal common law and not the varying common law of the individual states is, we 

think, entitled and necessary to be recognized as a basis for dealing in uniform standard 

with the environmental rights of a State against improper impairment by sources outside 

its domain.... Until the field has been made the subject of comprehensive legislation or 
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authorized administrative standards, only a federal common law basis can provide an 

adequate means for dealing with such claims as alleged federal rights.

406 U.S. at 107 n. 9, citing Texas v. Pankey, 441 F.2d 236, 241-242.

In City of Milwaukee, the Court revisited this dispute and addressed the expanded 

statutory provisions of the CWA regulating water pollution. The scope of the CWA amendments 

led the Court to reverse its decision in Illinois v. Milwaukee. In reaching this result, the Court 

concluded that Congress had elected to exercise its authority under federal law to occupy the 

field of water pollution regulation. As a result, the Court concluded that there was no basis for 

maintaining a federal common law of nuisance.

Congress has not left the formulation of appropriate federal standards to the courts 

through application of often vague and indeterminate nuisance concepts and maxims of 

equity jurisprudence, but rather has occupied the field through the establishment of a 

comprehensive regulatory program supervised by an expert administrative agency. The 

1972 Amendments to the Federal Water Pollution Control Act were not merely another 

law “touching interstate waters”... Rather, the Amendments were viewed by Congress as 

a “total restructuring” and “complete rewriting” of the existing water pollution legislation 

considered in that case.

451 U.S. at 317.

The Court’s analysis in Illinois v. Milwaukee made clear that federal common law was 

necessary to protect “the environmental rights of States against improper impairment by sources 

outside its domain.” 406 U.S. at 107, n. 9. In the context of interstate water pollution, nothing in 

the Court’s language or logic limits the reach of this conclusion to only navigable interstate 

waters. In City of Milwaukee, the Court found that the CWA was the “comprehensive regulatory 
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program” that “occupied the field” (451 U.S. 317) with regard to interstate water pollution, 

eliminating the basis for an independent common law of nuisance to address interstate water 

pollution. Since the federal common law of nuisance (as well as the statutory provisions 

regulating water pollution in the Federal Water Pollution Control Act) applied to interstate 

waters whether navigable or not, the CWA could only occupy the field of interstate water 

pollution if it too extended to non-navigable as well as navigable interstate waters. 

With regard to the specifics of interstate water pollution, the City of Milwaukee Court 

noted that, in Illinois v. Milwaukee, it had been concerned that Illinois did not have a forum in 

which it could protect its interests in abating water pollution from out of state, absent the 

recognition of federal common law remedies. 451 U.S. at 325. The Court then went on to 

analyze in detail the specific procedures created by the CWA “for a State affected by decisions 

of a neighboring State’s permit-granting agency to seek redress.” 451 U.S. at 326. The Court 

noted that “any State whose waters may be affected by the issuance of a permit” is to receive 

notice and the opportunity to comment on the permit. Id. (citing to CWA § 402(b)(3)(5)); In 

addition the Court noted provisions giving EPA the authority to veto and issue its own permits 

“if a stalemate between an issuing and objecting state develops.” Id. (citing to CWA §§ 

402(d)(2)(A),(4)). In light of these protections for States affected by interstate water pollution, 

the court concluded that

[t]he statutory scheme established by Congress provides a forum for the pursuit of such 

claims before expert agencies by means of the permit-granting process. It would be quite 

inconsistent with this scheme if federal courts were in effect to “write their own ticket” 

under the guise of federal common law after permits have already been issued and 

permittees have been planning and operating in reliance on them.
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451 U.S. at 326.

Nothing in the language or the reasoning of this discussion limits the applicability of 

these protections of interstate waters to navigable interstate waters or interstate waters connected 

to navigable waters. If these protections only applied to navigable interstate waters, a 

downstream State would unable to protect many of its waters from out of state water pollution. 

This would hardly constitute a comprehensive regulatory scheme that occupied the field of 

interstate water pollution.

For these reasons, the holdings and the reasoning of these decisions establish that the 

regulatory reach of the CWA extends to all interstate waters without regard to navigability.10

C. The Supreme Court’s Decisions in SWANCC and Rapanos Do Not Limit or

Constrain Clean Water Act Jurisdiction Over Non-navigable Interstate 

Waters.

As noted above, the Supreme Court recognized that Congress, in enacting the CWA, 

“intended to repudiate limits that had been placed on federal regulation by earlier water pollution 

control statutes and to exercise its powers under the Commerce Clause to regulate at least some 

waters that would not be deemed ‘navigable’ under the classical understanding of that term.” 

Riverside Bayview, 474 U.S. at 133; see also International Paper Co. v. Ouellette, 479 U.S. 481, 

486 n.6, (1987). In Riverside Bayview, and subsequently in SWANCC and Rapanos, the Court 

addressed the construction of the CWA terms “navigable waters” and “the waters of the United 

 10 Nothing in subsequent Supreme Court case law regarding interstate waters in any way conflicts with the 

agencies' interpretation. See International Paper v. Ouellette, 479 U.S. 481 (1987); Arkansas v. Oklahoma, 503 

U.S. 91 (1992). In both of these cases, the Court detailed how the CWA had supplanted the federal common law of 

nuisance to establish the controlling statutory scheme for addressing interstate water pollution disputes. Nothing in 

either decision limits the applicability of the CWA to interstate water pollution disputes involving navigable 

interstate waters or interstate waters connected to navigable waters.
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States.” In none of these cases did the Supreme Court address interstate waters, nor did it 

overrule prior Supreme Court precedent which addressed the interaction between the CWA and 

federal common law to address pollution of interstate waters. Therefore, the statute, even in light 

of SWANCC and Rapanos, does not impose an additional requirement that interstate waters must 

be water that is navigable for purposes of federal regulation under the Commerce Clause or 

connected to water that is navigable for purposes of federal regulation under the Commerce 

Clause to be jurisdictional waters for purposes of the CWA.

At the outset, it is worth noting that neither SWANCC nor Rapanos dealt with the 

jurisdictional status of interstate waters. Repeatedly in the SWANCC decision the Court 

emphasized that the question presented concerned the jurisdiction status of nonnavigable 

intrastate waters located in two Illinois counties. SWANCC 531 U.S. at 165-166, 171 (“we thus 

decline to... hold that isolated ponds, some only seasonal, wholly located within two Illinois 

counties fall under § 404(a) definition of navigable waters...”) (emphasis added). Nowhere in 

Justice Rehnquist’s majority opinion in SWANCC does the Court discuss the Court’s interstate 

water case law.11 The Court does not even discuss the fact that CWA jurisdictional regulations 

identify interstate waters as regulated waters of the United States. In fact, the repeated emphasis 

on the intrastate nature of the waters at issue can be read as an attempt to distinguish SWANCC

from the Court’s interstate water jurisprudence.

In Rapanos, the properties at issue were located entirely within the State of Michigan. 

547 U.S. 715, 762-764. Thus, the Court had no occasion to address the text of the CWA with 

respect to interstate waters or the agencies’ regulatory provisions concerning interstate waters. 

In addition, neither Justice Kennedy nor the plurality discusses the impact of their opinions on 

 11 It is worth noting the Justice Rehnquist was also the author of City of Milwaukee.
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the Court’s interstate waters jurisprudence. The plurality decision acknowledges that CWA 

jurisdictional regulations include interstate waters. 547 U.S. 715, 724. However, the plurality 

did not discuss in any detail its views as to the continued vitality of regulations concerning such 

waters.

Moreover, one of the analytical underpinnings of the SWANCC and Rapanos decisions is 

irrelevant to analysis of regulations asserting jurisdiction over interstate waters. In SWANCC, 

the Court declined to defer to agency regulations asserting jurisdiction over isolated waters 

because 

[w]here an administrative interpretation of a statute invokes the outer limits of Congress’ 

power, we expect a clear indication that Congress intended that result....This requirement 

stems from our prudential desire not to needlessly reach constitutional issues and our 

assumption that Congress does not casually authorize administrative agencies to push the 

limit of Congressional authority.... This concern is heightened where the administrative 

interpretation alerts the federal-state framework by permitting federal encroachment upon 

a traditional state power.

531 U.S. at 172-173 (citations omitted).

However, the Court’s analysis in Illinois v. Milwaukee and City of Milwaukee makes 

clear that Congress has broad authority to create federal law to resolve interstate water pollution 

disputes. As discussed above, the Court in Illinois v. Milwaukee, invited further federal 

legislation to address interstate water pollution, and in so doing concluded that state law was not 

an appropriate basis for addressing interstate water pollution issues. 406 U.S. at 107 n. 9 (citing 

Texas v. Pankey, 441 F.2d 236, 241-242). In City of Milwaukee, the Court indicated that central 

to its holding in Illinois v. Milwaukee was its concern “that Illinois did not have any forum to 
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protect its interests [in the matters involving interstate water pollution].” 451 U.S. 325. As 

discussed above, the Court cited with approval the statutory provisions of the CWA regulating 

water pollution as an appropriate means to address that concern. 

The City of Milwaukee and Illinois v. Milwaukee decisions make clear that assertion of 

federal authority to resolve disputes involving interstate waters does not alter “the federal-state 

framework by permitting federal encroachment on a traditional state power.” 531 U.S. at 173. 

“Our decisions concerning interstate waters contain the same theme. Rights in interstate streams, 

like questions of boundaries, have been recognized as presenting federal questions.” Illinois v. 

Milwaukee, 406 U.S. at 105 (internal quotations and citations omitted). 

The Supreme Court’s analysis in SWANCC and Rapanos materially altered the criteria for 

analyzing CWA jurisdictional issues for wholly intrastate waters. However, these decisions by 

their terms did not affect the body of case law developed to address interstate waters. The 

holdings in the Supreme Court’s interstate waters jurisprudence, in particular City of Milwaukee, 

apply CWA jurisdiction to interstate waters without regard to, or discussion of, navigability. In 

City of Milwaukee, the Court held that the CWA provided a comprehensive statutory scheme for 

addressing the consequences of interstate water pollution. Based on this analysis, the Court 

expressly overruled its holding in Illinois v. Milwaukee that the federal common law of nuisance 

would apply to resolving interstate water pollution disputes. Instead, the Court held that such 

disputes would now be resolved through application of the statutory provisions of the CWA 

regulating water pollution. 

It would be unreasonable to interpret SWANCC or Rapanos as overruling City of 

Milwaukee with respect to CWA jurisdiction over non-navigable interstate waters. Such an 

interpretation would result in no law to apply to water pollution disputes with regard to such 
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waters, unless one were to assume that the Court intended (without discussion or analysis) to 

restore the federal common law of nuisance as the law to apply in such matters. Moreover, 

SWANCC and Rapanos acknowledge that CWA regulatory jurisdiction extends to at least some 

non-navigable waters. See, e.g., 547 U.S. at 779 (Kennedy, J.). Neither the SWANCC Court 

nor the plurality or Kennedy opinions in Rapanos purports to set out the complete boundaries of 

CWA jurisdiction. See, e.g., 547 U.S. at 731 (“[w]e need not decide the precise extent to which 

the qualifiers ‘navigable’ and ‘of the United States’ restrict the coverage of the Act.”) (plurality 

opinion).

In addition, as the Supreme Court has repeatedly admonished, if a Supreme Court 

precedent has direct application in a case yet appears to rest on a rationale rejected in some other 

line of decisions, lower courts should follow the case which directly controls, leaving to the 

Supreme Court the prerogative of overruling its precedents. Agostino v. Felton, 521 U.S. 203, 

237 (1997); United States v. Hatter, 532 U.S. 557, 566-567(1981). Moreover, when the 

Supreme Court overturns established precedent, it is explicit. See, Lawrence v. Texas, 539 U.S. 

558, 578 (“Bowers was not correct when it was decided, and it is not correct today. It ought not 

to remain binding precedent. Bowers v. Hardwick should be and now is overruled.”). 

D. The Agencies’ Longstanding Interpretation of the Term “Navigable Waters” 

to Include “Interstate Waters” 

EPA, the agency charged with implementing the CWA, has always interpreted the 1972 

Act to cover interstate waters. Final Rules, 38 Fed. Reg. 13528 (May 22, 1973) (the term 

“waters of the United States” includes “interstate waters and their tributaries, including adjacent 

wetlands”). While the Corps of Engineers initially limited the scope of coverage for purposes of 

section 404 of the CWA to those waters that were subject to the Rivers and Harbors Act of 1899, 
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after a lawsuit, the Corps amended its regulations to provide for the same definition of “waters of 

the United States” that EPA’s regulations had always established. In 1975, the Corps’ revised 

regulations defined “navigable waters” to include “[i]nterstate waters landward to their ordinary 

high water mark and up to their headwaters.” In their final rules promulgated in 1977, the Corps 

adopted EPA’s definition and included within the definition of “waters of the United States” 

“interstate waters and their tributaries, including adjacent wetlands.” The preamble provided an 

explanation for the inclusion of interstate waters:

The affects [sic] of water pollution in one state can adversely affect the quality of 

the waters in another, particularly if the waters involved are interstate. Prior to 

the FWPCA amendments of 1972, most federal statutes pertaining to water 

quality were limited to interstate waters. We have, therefore, included this third 

category consistent with the Federal government’s traditional role to protect these 

waters from the standpoint of water quality and the obvious effects on interstate 

commerce that will occur through pollution of interstate waters and their 

tributaries.

Final Rules, 42 Fed. Reg. 37122 (July 19, 1977).

The legislative history similarly provides support for the agencies’ interpretation. 

Congress in 1972 concluded that the mechanism for controlling discharges and, thereby abating 

pollution, under the FWPCA and Refuse Act “has been inadequate in every vital aspect.” S. 

Rep. No. 414, 92d Cong., 1st Sess. 7 (1972). The Senate Committee on Public Works reported 

that development of water quality standards, assigned to the States under the 1965 FWPCA 

Amendments, “is lagging” and the “1948 abatement procedures, and the almost total lack of 

enforcement,” prompted the search for “more direct avenues of action against water polluters and 
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water pollution.” Id. at 5. The Committee further concluded that although the Refuse Act permit 

program created in 1970 “seeks to establish this direct approach,” it was too weak because it 

applied only to industrial polluters and too unwieldy because the authority over each permit 

application was divided between two Federal agencies. See id. at 5; see also id. at 70-72 

(discussing inadequacies of Refuse Act program). 

In light of the poor success of those programs, the Committee recommended a more 

direct and comprehensive approach which, after amendment in conference, was adopted in the 

1972 Act. The text, legislative history and purpose of the 1972 Amendments all show an intent –

through the revisions – to broaden, improve and strengthen, not to curtail, the federal water 

pollution control program that had existed under the Refuse Act and FWPCA.12 The 1972 

FWPCA Amendments were “not merely another law ‘touching interstate waters’” but were

“viewed by Congress as a ‘total restructuring’ and ‘complete rewriting’ of the existing water 

pollution legislation.”13

As the legislative history of the 1972 Act confirms, Congress’ use of the term “waters of 

the United States” was intended to repudiate earlier limits on the reach of federal water pollution 

efforts: “The conferees fully intend that the term ‘navigable waters’ be given the broadest 

possible constitutional interpretation unencumbered by agency determinations which have been 

made or may be made for administrative purposes.” See S. Conf. Rep. No. 1236, 92d Cong., 2d 

 12 See id. at 9 (“The scope of the 1899 Refuse Act is broadened; the administrative capability is strengthened.”); 

id. at 43 (“Much of the Committee’s time devoted to this Act centered on an effort to resolve the existing water 

quality program and the separate pollution program developing under the 1899 Refuse Act.”). Congress made an 

effort “to weave” the Refuse Act permit program into the 1972 Amendments, id. at 71, as the statutory text shows. 

See 33 U.S.C. 1342(a) (providing that each application for a permit under 33 U.S.C. 407, pending on October 18, 

1972, shall be deemed an application for a permit under 33 U.S.C. 1342(a)).

13 City of Milwaukee v. Illinois, 451 U.S. at 317; see also id. at 318 (holding that the CWA precluded federal 

common-law claims because “Congress’ intent in enacting the [CWA] was clearly to establish an all-encompassing 

program of water pollution regulation”); Middlesex County Sewerage Auth. v. National Sea Clammers Ass'n, 453 

U.S. 1, 22 (1981) (existing statutory scheme “was completely revised” by enactment of the CWA). 
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Sess. 144 (1972). The House and Senate Committee Reports further elucidate the Conference 

Committee’s rationale for removing the word “navigable” from the definition of “navigable 

waters,” in 33 U.S.C. § 1362(7). The Senate report stated:

The control strategy of the Act extends to navigable waters. The definition of this term 

means the navigable waters of the United States, portions thereof, tributaries thereof, and 

includes the territorial seas and the Great Lakes. Through a narrow interpretation of the 

definition of interstate waters the implementation of the 1965 Act was severely limited. 

Water moves in hydrologic cycles and it is essential that discharge of pollutants be 

controlled at the source. Therefore, reference to the control requirements must be made 

the navigable waters, portions thereof, and their tributaries.

See S. Rep. 414, 92d Cong., 1st Sess. 77 (1971); see also H.R. Rep. No. 911, 92d Cong., 2d Sess. 

131 (1972) (“The Committee fully intends that the term “navigable waters” be given the broadest 

possible constitutional interpretation unencumbered by agency determinations which have been 

made or may be made for administrative purposes.”). These passages strongly suggest that 

Congress intended to expand federal protection of waters. There is no evidence that Congress 

intended to exclude interstate waters which were protected under federal law if they were not 

water that is navigable for purposes of federal regulation under the Commerce Clause or 

connected to water that is navigable for purposes of federal regulation under the Commerce 

Clause. Such an exclusion would be contrary to all the stated goals of Congress in enacting the 

sweeping amendments which became the CWA.

The CWA was enacted in 1972. EPA’s contemporaneous regulatory definition of 

“waters of the United States,” promulgated in 1973, included interstate waters The definition 

has been EPA’s interpretation of the geographic jurisdictional scope of the CWA for 
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approximately 40 years. Congress has also been aware of and has supported the Agency’s 

longstanding interpretation of the CWA. “Where ‘an agency’s statutory construction has been 

fully brought to the attention of the public and the Congress, and the latter has not sought to alter 

that interpretation although it has amended the statute in other respects, then presumably the 

legislative intent has been correctly discerned.’” North Haven Board of Education v. Bell, 102 S. 

Ct. 1912, 1924 (1982) (quoting United States v. Rutherford, 99 S. Ct. 2470 (1979) (internal 

quotes omitted)).

The 1977 amendments to the CWA were the result of Congress’ thorough analysis of the 

scope of CWA jurisdiction in light of EPA and Corps regulations. The 1975 interim final 

regulations promulgated by the Corps in response to NRDC v. Callaway14, aroused considerable 

congressional interest. Hearings on the subject of Section 404 jurisdiction were held in both the 

House and the Senate.15 An amendment to limit the geographic reach of Section 404 to waters

that are navigable for purposes of federal regulation under the Commerce Clauses and their 

adjacent wetlands was passed by the House, 123 Cong. Rec. 10434 (1977), defeated on the floor 

of the Senate, 123 Cong. Rec. 26728 (1977), and eliminated by the Conference Committee, H.R. 

Conf. Rep. 95-830, 95th Cong., 1st Sess. 97-105 (1977). Congress rejected the proposal to limit 

the geographic reach of Section 404 because it wanted a permit system with “no gaps” in its 

protective sweep. 123 Cong. Rec. 26707 (1977) (remarks of Sen. Randolph). Rather than alter 

the geographic reach of Section 404, Congress amended the statute by exempting certain 

 14 40 Fed.Reg. 31320, 31324 (July 25, 1975).

15 Section 404 of the Federal Water Pollution Control Act Amendments of 1972: Hearings Before the Senate 

Comm. on Public Works, 94th Cong., 2d Sess. (1976); Development of New Regulations by the Corps of Engineers, 

Implementing Section 404 of the Federal Water Pollution Control Act Concerning Permits for Disposal of Dredge 

or Fill Material: Hearings Before the Subcomm. on Water Resources of the House Comm. on Public Works and 

Transportation, 94th Cong., 1st Sess. (1975).
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activities -- most notably certain agricultural and silvicultural activities -- from the permit 

requirements of Section 404. See 33 U.S.C. § 1344(f).

Other evidence abounds to support the conclusion that when Congress rejected the 

attempt to limit the geographic reach of Section 404, it was well aware of the jurisdictional scope 

of EPA and the Corps’ definition of “waters of the United States.” For example, Senator Baker 

stated (123 Cong. Rec. 26718 (1977)):

Interim final regulations were promulgated by the corps [on] July 25, 1975. . . .

Together the regulations and [EPA] guidelines established a management 

program that focused the decisionmaking process on significant threats to aquatic 

areas while avoiding unnecessary regulation of minor activities. On July 19, 

1977, the corps revised its regulations to further streamline the program and 

correct several misunderstandings. . . .

Continuation of the comprehensive coverage of this program is essential for the 

protection of the aquatic environment. The once seemingly separable types of 

aquatic systems are, we now know, interrelated and interdependent. We cannot 

expect to preserve the remaining qualities of our water resources without 

providing appropriate protection for the entire resource.

Earlier jurisdictional approaches under the [Rivers and Harbors Act] established 

artificial and often arbitrary boundaries . . . .

This legislative history leaves no room for doubt that Congress was aware of the 

agencies’ definition of navigable waters. While there was controversy over the assertion of 

jurisdiction over all adjacent wetlands and some non-adjacent wetlands, the agencies’ assertion 

of CWA jurisdiction over interstate waters was uncontroversial.
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Finally, the constitutional concerns which led the Supreme Court to decline to defer to 

agency regulations in SWANCC and Rapanos are not present here where the agency is asserting 

jurisdiction over interstate waters. In SWANCC, the Court declined to defer to agency 

regulations asserting jurisdiction over non-adjacent, non-navigable, intrastate waters because the 

Court felt such an interpretation of the statute invoked the outer limits of Congress’ power. The 

Court’s concern “is heightened where the administrative interpretation alerts the federal-state 

framework by permitting federal encroachment upon a traditional state power.” 531 U.S. at 172-

173 (citations omitted). Authority over interstate waters is squarely within the bounds of 

Congress’ Commerce Clause powers.16 Further, the federal government is in the best position to 

address issues which may arise when waters cross State boundaries, so this interpretation does 

not disrupt the federal-state framework in the manner the Supreme Court feared that the assertion 

of jurisdiction over a non-adjacent, non-navigable, intrastate body of water based on the presence 

of migratory birds did. The Supreme Court’s analysis in Illinois v. Milwaukee and City of 

Milwaukee makes clear that Congress has broad authority to create federal law to resolve 

interstate water pollution disputes. Therefore, as discussed in Section II.B above, it is 

appropriate for the agencies to adopt an interpretation of the extent of CWA jurisdiction over 

interstate waters that gives full effect to City of Milwaukee unless and until the Supreme Court 

elects to revisit its holding in that case.

Thus, based on the language of the statute, the statutory history, the legislative history, 

and the caselaw, the agencies’ continue their longstanding interpretation of “navigable waters” to 

include interstate waters.

 16 In Illinois v. Milwaukee, the Supreme Court noted that "Congress has enacted numerous laws touching interstate 

waters." 406 U.S. at 101.
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Tributaries

The agencies analyzed the science to determine whether an ordinary high water mark 

provides a “reasonable measure of whether specific minor tributaries bear a sufficient nexus with 

other regulated waters to constitute ‘navigable waters’ under the Act.” 547 U.S. at 781. Justice 

Kennedy provides an approach for determining what constitutes a “significant nexus” that can 

serve as a basis for statutory jurisdiction. Again, the four justices who signed on to Justice 

Stevens’ opinion would have upheld jurisdiction under the agencies’ existing regulations and 

stated that they would uphold jurisdiction under either the plurality or Justice Kennedy’s opinion. 

Justice Kennedy concludes that Riverside Bayview and SWANCC “establish the framework for” 

determining whether an assertion of jurisdiction constitutes a reasonable interpretation of 

“navigable waters” - “the connection between a non-navigable water or wetland and a navigable 

water may be so close, or potentially so close, that the Corps may deem the water or wetland a 

‘navigable water’ under the Act;” “[a]bsent a significant nexus, jurisdiction under the Act is 

lacking.” 547 U.S. at 767. “The required nexus must be assessed in terms of the statute’s goals 

and purposes. Congress enacted the law to ‘restore and maintain the chemical, physical, and 

biological integrity of the Nation’s waters,’ 33 U.S.C. § 1251(a), and it pursued that objective by 

restricting dumping and filling in ‘navigable waters,’ §§ 1311(a), 1362(12).” Id. at 779. Justice 

Kennedy provided further guidance for determining whether wetlands should be considered to 

possess the requisite nexus in the context of assessing whether wetlands are jurisdictional: “if the 

wetlands, either alone or in combination with similarly situated [wetlands] in the region, 

significantly affect the chemical, physical, and biological integrity of other covered waters more 

readily understood as ‘navigable.’” Id. at 780. While Justice Kennedy focused on adjacent 

wetlands in light of the facts of the cases before him, it is reasonable to utilize the same standard 
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for tributaries. In addition, Justice Kennedy stated that “[t]hrough regulation or adjudication, the 

Corps may choose to identify categories of tributaries that, due to their volume of flow (either 

annually or on average), their proximity to navigable waters, or other relevant considerations, are 

significant enough that wetlands adjacent to them are likely, in the majority of cases, to perform 

important functions for an aquatic system incorporating navigable waters.” 547 U.S. at 780-81. 

As discussed in the preamble and Appendix A, based on a detailed examination of the scientific 

literature, the agencies concluded that tributaries as they propose to define them perform the 

requisite functions identified by Justice Kennedy for them to be considered, as a category, to be 

waters of the United States.

Assertion of jurisdiction over tributaries with a bed and banks and OHWM is also 

consistent with Rapanos because five Justices did not question the Corps’ and EPA’s current 

regulations, which assert jurisdiction over non-navigable tributaries of traditional navigable 

waters and interstate waters. The four justices joining Justice Stevens’ dissenting opinion would 

have upheld the agencies’ regulations as applied as a reasonable interpretation of the CWA. 

Justice Kennedy’s opinion focuses on determining when an adjacent wetland is jurisdictional. 

Underlying his analysis is the premise that the tributaries to which the wetlands are adjacent are 

jurisdictional. Indeed, Justice Kennedy also does not question the regulation of tributaries with 

an OHWM. Therefore, it is reasonable to conclude that five justices would uphold the assertion 

of jurisdiction over tributaries with an OHWM to a traditional navigable water or interstate 

water.

First, Justice Kennedy rejected the plurality’s approach that only “relatively permanent” 

tributaries are within the scope of CWA jurisdiction. Instead, Justice Kennedy concluded that

“Congress could draw a line to exclude irregular waterways, but nothing in the statute suggests it 
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has done so;” in fact, he states that Congress has done “quite the opposite.” Id. at 2242. Further, 

Justice Kennedy concludes, based on “a full reading of the dictionary definition” of “water,” that 

“the Corps can reasonably interpret the Act to cover the paths of such impermanent streams.” 

Id. at 2243 (emphasis added). First, Justice Kennedy notes that the term “waters” can mean 

“flood or inundation,” according to the Webster’s Second definition, and that these events are 

“impermanent by definition.” Second, even looking to the plurality’s preferred dictionary 

definition of “waters,” i.e., “water as found in streams and bodies forming geographical features 

such as oceans, rivers, and lakes,” Justice Kennedy notes that “intermittent flow can constitute a 

stream.” Id. at 2243. And finally, Justice Kennedy notes that the plurality’s reference to the 

statement by the Riverside Bayview Court comparing wetlands to “rivers, streams, and other 

hydrographic features more conventionally identifiable as ‘waters’ ... could just as well refer to 

intermittent streams.” Id. (citations omitted). Even in Justice Kennedy’s rejection of Justice 

Steven’s dissent it is clear that he only rejects the broad scope of jurisdiction over wetlands 

without further analysis, not jurisdiction over tributaries regardless of their size or 

characteristics: “the dissent would permit federal regulation whenever wetlands lie alongside a 

ditch or drain, however remote and insubstantial, that eventually may flow into traditional 

navigable waters. The deference owed to the Corps’ interpretation of the statute does not extend 

so far.” Id. at 2246. Tellingly, in that passage Justice Kennedy expresses concern with the 

assertion of jurisdiction over the wetlands without a conclusion that they have a significant 

nexus, but does not question the regulation of the remote “ditch or drain.”

Justice Kennedy also discussed in detail the existing regulation of tributaries without 

concluding that it was inconsistent with the scope of the Act, in direct contrast to his concerns 

with respect to the regulation of adjacent wetlands. Justice Kennedy described the Corps’ 
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standard for asserting jurisdiction over tributaries: “the Corps deems a water a tributary if it feeds 

into a traditional navigable water (or a tributary thereof) and possesses an ordinary high-water 

mark.” Id. at 2248-49. Justice Kennedy concluded that this standard “presumably provides a 

rough measure of the volume and regularity of flow.” Id. In addition, if it is applied reasonably 

consistently, the Corps’ existing standard for tributaries “may well provide a reasonable measure 

of whether specific minor tributaries bear a sufficient nexus with other regulated waters to 

constitute ‘navigable waters’ under the Act.” Id. at 2249. 

Justice Kennedy then goes on to determine the scope of jurisdiction over wetlands, and 

his conclusions rely on the premise that the tributaries themselves are jurisdictional since his 

analysis is entirely focused on whether certain adjacent wetlands are jurisdictional. Justice 

Kennedy concludes that, “[a]s applied to wetlands adjacent to navigable-in-fact waters, the 

Corps’ conclusive standard for jurisdiction rests upon a reasonable inference of ecologic 

interconnection, and the assertion of jurisdiction for those wetlands is sustainable under the Act 

by showing adjacency alone.” Id. (emphasis added). While Justice Kennedy also states that the 

same reasoning “could apply equally to wetlands adjacent to certain major tributaries[,]” the 

Corps would need to identify categories of tributaries that are “significant enough” such that 

wetlands adjacent to them are likely to perform important functions relating to an aquatic system 

containing navigable waters. Id. Justice Kennedy makes no such recommendation that the EPA 

and the Corps need to identify categories of tributaries that are likely to perform important 

functions in order to assert jurisdiction over the tributaries themselves.

Justice Kennedy did express a concern with the Corps’s assertion of jurisdiction over 

tributaries with an OHWM based on a 2004 U.S. Government Accountability Office (GAO) 

report that found variations in Corps’ district practices. In 2005, the Corps issued a regulatory 
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guidance letter (RGL 05-05) to Corps districts on OHWM identification that was designed to 

ensure more consistent practice. The Corps has also issued documents to provide additional 

technical assistance for problematic OHWM delineations. See, e.g., R.W. Lichvar and S.M. 

McColley, U.S. Army Corps of Engineers, A Field Guide to the Identification of the Ordinary 

High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation 

Manual, ERDC/CRREL TR-08-12 (2008). Most importantly, the agencies propose today for the 

first time a regulatory definition of “tributary.” The definition expressly addresses some of the 

issues with respect to identification of an OHWM that caused many of the inconsistencies 

reported by the GAO. For example, this proposed regulation is clear that a water which 

otherwise meets the proposed definition of tributary, remains a jurisdictional tributary even if 

there are natural or man-made breaks in the OHWM. The proposed definition also provides a 

non-exclusive list of examples of breaks in the OHWM to assist in clearly and consistently 

determining what meets the definition of tributary.

Adjacent Waters

The CWA explicitly establishes authority over adjacent wetlands. Under Section 404(g), 

states are authorized to assume responsibility for administration of the Section 404 permitting 

program with respect to “navigable waters (other than those waters which are presently used, or 

are susceptible to use in their natural condition or by reasonable improvement as a means to 

transport interstate or foreign commerce shoreward to their ordinary high water mark, including 

all waters which are subject to the ebb and flow of the tide shoreward to their mean high water 

mark, or mean higher high water mark on the west coast, including wetlands adjacent thereto).” 

33 U.S.C. 1344(g)(1) (emphasis added). While this provision mainly serves as a limitation on 
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the scope of waters for which States may be authorized to issue permits, it also shows that 

Congress was concerned with the protection of adjacent wetlands and recognized their important 

role in protecting downstream traditional navigable waters. Indeed, the existing definition of 

adjacency was developed in recognition of the integral role wetlands play in broader aquatic 

ecosystems:

The regulation of activities that cause water pollution cannot rely on . . . artificial lines . . . 

but must focus on all waters that together form the entire aquatic system. Water moves in 

hydrologic cycles, and the pollution of this part of the aquatic system, regardless of 

whether it is above or below an ordinary high water mark, or mean high tide line, will 

affect the water quality of the other waters within that aquatic system. For this reason, the 

landward limit of Federal jurisdiction under Section 404 must include any adjacent 

wetlands that form the border of or are in reasonable proximity to other waters of the 

United States, as these wetlands are part of this aquatic system. 

42 Fed. Reg. 37128 (1977). 

As the Supreme Court found in United States v. Riverside Bayview Homes, Inc., “the 

evident breadth of congressional concern for protection of water quality and aquatic ecosystems 

suggests that it is reasonable for the Corps to interpret the term ‘waters’ to encompass wetlands 

adjacent to waters as more conventionally defined.” 474 U.S. 121, 133 (1985).

In upholding the Corps’ judgment about the relationship between waters and their 

adjacent wetlands, the Supreme Court in Riverside Bayview acknowledged that the agencies’ 

regulations take into account functions provided by wetlands in support of this relationship. 

“Adjacent wetlands may ‘serve significant natural biological functions, including food chain 

production, general habitat, and nesting, spawning, rearing and resting sites for aquatic . . . 
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species.’” 474 U.S. at 133 (citing § 320.4(b)(2)(i)). The Court further stated that the Corps had 

reasonably concluded that “wetlands adjacent to lakes, rivers, streams, and other bodies of water 

may function as integral parts of the aquatic environment even when the moisture creating the 

wetlands does not find its source in the adjacent bodies of water.” 474 U.S. at 134-35. A 

majority of the Supreme Court which decided Rapanos continues to find the agencies’ regulatory 

definition of adjacent wetlands reasonable. Justice Kennedy stated: 

As the Court noted in Riverside Bayview, ‘the Corps has concluded that wetlands may 

serve to filter and purify water draining into adjacent bodies of water, 33 CFR § 

320.4(b)(2)(vii)(1985), and to slow the flow of surface runoff into lakes, rivers, and 

streams and thus prevent flooding and erosion, see §§ 20.4(b)(2)(iv) and (v).’ Where 

wetlands perform these filtering and runoff-control functions, filling them may increase 

downstream pollution, much as a discharge of toxic pollutants would. . . . In many cases, 

moreover, filling in wetlands separated from another water by a berm can mean that flood 

water, impurities, or runoff that would have been stored or contained in the wetlands will 

instead flow out to major waterways. With these concerns in mind, the Corps’ definition 

of adjacency is a reasonable one, for it may be the absence of an interchange of waters 

prior to the dredge and fill activity that makes protection of the wetlands critical to the 

statutory scheme.

126 S.Ct at 2245-46. 

The four dissenting justices similarly concluded:

The Army Corps has determined that wetlands adjacent to tributaries of traditionally 

navigable waters preserve the quality of our Nation’s waters by, among other things, 

providing habitat for aquatic animals, keeping excessive sediment and toxic pollutants
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out of adjacent waters, and reducing downstream flooding by absorbing water at times of 

high flow. The Corps’ resulting decision to treat these wetlands as encompassed within 

the term ‘waters of the United States’ is a quintessential example of the Executive’s 

reasonable interpretation of a statutory provision. 

126 S.Ct. at 2252-53 (citing Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 

467 U. S. 837, 842-845 (1984)). 

For those wetlands adjacent to (a)(1) through (a)(3) waters, Justice Kennedy concluded in 

Rapanos that the agencies’ existing regulation “rests upon a reasonable inference of ecologic 

interconnection, and the assertion of jurisdiction for those wetlands is sustainable under the Act 

by showing adjacency alone.” 547 U.S. at 780. For all other adjacent waters, including adjacent 

wetlands, Justice Kennedy provided a framework for establishing categories of waters which are 

per se “waters of the United States.” First, he provided that wetlands are jurisdictional if they 

“either alone or in combination with similarly situated lands in the region, significantly affect the 

chemical, physical, and biological integrity of other covered waters more readily understood as 

‘navigable.’” 547 U.S. at 780. While the issue was not before the Supreme Court, it is 

reasonable to also assess whether non-wetland waters have a significant nexus, as Justice 

Kennedy’s opinion makes clear that a significant nexus is a touchstone for CWA jurisdiction. 

Next, Justice Kennedy stated that “[t]hrough regulation or adjudication, the Corps may choose to 

identify categories of tributaries that, due to their volume of flow (either annually or on average), 

their proximity to navigable waters, or other relevant considerations, are significant enough that

wetlands adjacent to them are likely, in the majority of cases, to perform important functions for 

an aquatic system incorporating navigable waters.” 547 U.S. at 780-81. 
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The significant nexus standard and the category standard of Justice Kennedy’s opinion

should be read together. The agencies have determined that adjacent waters as defined in today’s 

proposed rule, alone or in combination with other adjacent waters in a watershed that drains to a 

traditional navigable water, interstate water or the territorial seas, to significantly affect the 

chemical, physical and biological integrity of those waters. As explained in more detail in 

Section H, below, the proposed rule interprets the phrase “in the region” to mean the watershed 

that drains to the nearest traditional navigable water or interstate water through a single point of 

entry. The agencies have determined that because the movement of water from watershed 

drainage basins to river networks and lakes shapes the development and function of these

systems in a way that is critical to their long term health, the watershed is a reasonable and 

technically appropriate interpretation of Justice Kennedy’s standard. 

The agencies have concluded that all waters that meet the proposed definition of 

“adjacent” are similarly situated for purposes of analyzing whether they, in the majority of cases, 

have a significant nexus to an (a)(1) through (a)(3) water. Based on the agencies’ review of the 

scientific literature, we have concluded that these waters, when bordering, contiguous or located 

in the floodplain or riparian area, or when otherwise meeting the definition of “adjacent,” 

provide many similar functions that significantly affect the chemical, physical, or biological 

integrity of traditional navigable waters, interstate waters, or the territorial seas. Further, because 

the proposed definition generally focuses on the location of the waters (i.e., those that are 

located near (a)(1) through (a)(5) waters), interpreting the term "similarly situated" to include all 

adjacent waters, as defined in the proposed rule, is reasonable and consistent with the science. 

The geographic position of an “adjacent” water relative to the tributary is indicative of the 

relationship to it, with many of its defining characteristics resulting from the movement of 
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materials and energy between the categories of waters. The scientific literature documents that 

waters that are adjacent to (a)(1) through (a)(5) waters, including wetlands, oxbow lakes and 

adjacent ponds, are integral parts of stream networks because of their ecological functions and 

how they interact with each other, and with downstream traditional navigable waters, interstate 

waters, or the territorial seas. In other words, tributaries and their adjacent waters, and the 

downstream traditional navigable waters, interstate waters, and territorial seas into which those 

waters flow, are an integrated ecological system, and discharges of pollutants, including 

discharges of dredged or fill material, into any component of that ecological system, must be 

regulated under the CWA to restore and maintain the chemical, physical, or biological integrity 

of these waters.

While Justice Kennedy generally thought that categories of jurisdictional adjacent waters 

would be most likely based on the flow of the tributary, based on the science, as summarized 

below, the agencies have concluded that wetlands and waters adjacent to all tributaries that meet 

the proposed definition of “tributary” provide vital functions for downstream traditional 

navigable waters, interstate waters or the territorial seas. In particular, the scientific literature 

supports the conclusion that waters adjacent to all tributaries as defined in section (a)(5) have a 

significant nexus to waters described in subsections (a)(1) through (3). Because smaller streams, 

whether perennial, intermittent, or ephemeral, are much more common than larger streams, the 

volume of a stream’s flow is not the best measure of its contribution to the chemical, physical or 

biological integrity of downstream waters. Report at 48. As discussed in more detail in 

Appendix A, small streams cumulatively exert a strong influence on downstream waters, partly 

by collectively providing a substantial amount of the river’s water, id. at 52-53, but also by 

playing unique roles that large streams typically do not, including providing habitat for aquatic 
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macroinvertebrates which help maintain the health of the downstream water. Waters adjacent to 

those small tributary streams, therefore, also significantly effect (a)(1) through (a)(3) waters 

through the movement of energy and materials between adjacent waters and those tributaries, 

resulting ultimately in downstream effects on the chemical, physical, and biological integrity of 

the (a)(1) through (a)(3) waters.

“Other Waters”

In Rapanos, Justice Kennedy provides an approach for determining what constitutes a 

“significant nexus” that can serve as a basis for defining “waters of the United States” through 

regulation. Again, the four justices who signed on to Justice Stevens’ opinion would have 

upheld jurisdiction under the agencies’ existing regulations and stated that they would uphold 

jurisdiction under either the plurality or Justice Kennedy’s opinion. Justice Kennedy provided 

guidance for determining whether these wetlands should be considered to possess the requisite 

nexus in the context of assessing whether wetlands are jurisdictional: “if the wetlands, either 

alone or in combination with similarly situated [wetlands] in the region, significantly affect the 

chemical, physical, and biological integrity of other covered waters more readily understood as 

‘navigable.’” Id. at 780. While Justice Kennedy focused on adjacent wetlands in light of the facts 

of the cases before him; in combination with the Court’s guidance in SWANCC, it is reasonable 

to apply the same standard to other waters such as ponds, lakes and non-adjacent wetlands that 

may have a significant nexus to a traditional navigable water, interstate water, or the territorial 

seas.

The proposed rule includes a definition of significant nexus that is consistent with Justice 

Kennedy’s approach to assess the nexus by focusing on the chemical, physical, and biological 
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roles of waters in supporting the objective and goals of the Act. In characterizing the significant 

nexus standard, Justice Kennedy stated: “The required nexus must be assessed in terms of the 

statute’s goals and purposes. Congress enacted the [CWA] to ‘restore and maintain the 

chemical, physical, and biological integrity of the Nation’s waters’ . . . .” 547 U.S. at 779. It is 

reasonable to interpret Justice Kennedy as intending the required nexus to exist when, for 

example, the pollution or destruction of a wetland, or group of similarly situated wetlands, would 

impact the integrity of the fish population of a downstream traditional navigable water even if it 

would have no effect on the physical structure of the downstream water. It is clear that the 

statute, and thus Justice Kennedy’s standard, is intended to protect the integrity of each of the 

fundamental attributes of the nation’s waters and that intent would be subverted if waters were 

protected under the CWA only if they had effects on every attribute at once of a traditional 

navigable water, interstate water, or territorial sea. Justice Kennedy’s standard is also consistent 

with basic scientific principles understood about how to restore and maintain the integrity of 

aquatic ecosystems.

Justice Kennedy’s opinion provides guidance pointing to many functions of waters that 

might demonstrate a significant nexus, such as sediment trapping, nutrient recycling, pollutant 

trapping and filtering, retention or attenuation of flood waters, runoff storage, and provision of 

habitat. 547 U.S. at 775, 779-80. Furthermore, Justice Kennedy recognized that a hydrologic 

connection is not necessary to establish a significant nexus, because in some cases the lack of a 

hydrologic connection would show the significance of a water to the aquatic system, such as 

retention of flood waters or pollutants that would otherwise flow downstream to the traditional 

navigable water or interstate water. Id. at 775. Finally, Justice Kennedy was clear that the 
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requisite nexus must be more than “speculative or insubstantial” in order to be significant. Id. at 

780. 

Similarly Situated 

For purposes of analyzing the significant nexus of tributaries and adjacent waters, 

tributaries that meet the proposed definition of “tributary” in a watershed draining to an (a)(1) 

through (a)(3) water are similarly situated, and adjacent waters that meet the proposed definition 

of “adjacent” in a watershed draining to an (a)(1) through (a)(3) water are similarly situated. 

That is reasonable because the agencies are identifying characteristics of these waters through 

the regulation and documenting the science that demonstrates that these defined tributaries and 

defined adjacent waters provide similar functions in the watershed. As stated above, the 

functions of the tributaries are inextricably linked and have a cumulative effect on the integrity 

of the downstream traditional navigable water or interstate water. There is also an obvious 

locational relationship between the (a)(1), (a)(2) or (a)(3) water and the streams, lakes, and 

wetlands that meet the definition of tributaries and the definition of adjacent waters; these waters 

have a clear linear relationship resulting from the simple existence of the channel itself and the 

direction of flow. See Appendix A, Scientific Analysis.

“Other waters,” on the other hand, constitute a broad range of different types of waters 

performing different functions. In light of the range and degree of functions performed by 

waters that are neither tributaries nor adjacent waters under today’s proposed rule, the agencies 

propose a definition of similarly situated which takes into account similarity of functions 

provided and situation in the landscape. Since the focus of the significant nexus standard is on 

protecting the chemical, physical and biological integrity of the nation’s waters, the agencies 

propose to interpret the phrase “similarly situated” first in terms of whether the functions 
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provided by the particular other waters are similar and, therefore, whether such “other waters”

are collectively influencing the chemical, physical, or biological integrity of downstream waters. 

There are many functions of waters that might demonstrate a significant nexus, such as sediment 

trapping, nutrient recycling, pollutant trapping and filtering, retention or attenuation of flood 

waters, runoff storage, and provision of habitat. 547 U.S. at 775, 779-80. This approach is 

consistent not only with the significant nexus standard, but with the science of aquatic systems.

The lack of a hydrologic connection between “other waters” and traditional navigable 

waters, interstate waters or the territorial seas may demonstrate the presence of a significant 

nexus between such waters, as Justice Kennedy recognized in his opinion. “Other waters”

frequently function alone or cumulatively with similarly situated other waters in the region to 

capture runoff, rain water, or snowmelt and thereby protect the integrity of downstream waters 

by reducing potential flooding or trapping pollutants that would otherwise reach a traditional 

navigable water or interstate water. 547 U.S. at 775. Such waters can be crucial in controlling 

flooding as well as in maintaining water quality by trapping or transforming pollutants such as 

excess nutrients or sediment, for example, or retaining precipitation or snow melt, thereby 

reducing contamination or flooding of traditional navigable waters, interstate waters or the 

territorial seas. 

Significant Nexus

The agencies propose to define the term “significant nexus” consistent with language in 

SWANCC and Rapanos. The proposed definition of “significant nexus” at (c)(7) relies most 

significantly on Justice Kennedy’s Rapanos opinion which recognizes that not all waters have 

this requisite connection to waters covered by paragraphs (a)(1) through (a)(3) of the proposed 

regulations. Justice Kennedy was clear that the requisite nexus must be more than “speculative 
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or insubstantial,” Rapanos, at 780, in order to be significant and the proposed rule defines

significant nexus in precisely those terms. In Rapanos, Justice Kennedy stated that in both the 

consolidated cases before the Court the record contained evidence suggesting the possible 

existence of a significant nexus according to the principles he identified. Justice Kennedy 

concluded that “the end result in these cases and many others to be considered by the Corps may 

be the same as that suggested by the dissent, namely, that the Corps’ assertion of jurisdiction is 

valid.” Justice Kennedy remanded the cases because neither the agency nor the reviewing courts 

properly applied the controlling legal standard – whether the wetlands at issue had a significant 

nexus. Justice Kennedy was clear however, that “[m]uch the same evidence should permit the 

establishment of a significant nexus with navigable-in-fact waters, particularly if supplemented 

by further evidence about the significance of the tributaries to which the wetlands are 

connected.” Id. at XX

With respect to one of the wetlands at issue in the consolidated Rapanos cases, Justice 

Kennedy stated the record also contained evidence bearing on the jurisdictional inquiry. The 

Corps noted in deciding the administrative appeal that “[b]esides the effects on wildlife habitat 

and water quality, the [district office] also noted that the project would have a major, long-term 

detrimental effect on wetlands, flood retention, recreation and conservation and overall ecology.” 

Id. The Corps’ evaluation further noted that by “eliminat[ing] the potential ability of the wetland 

to act as a sediment catch basin,” the proposed project “would contribute to increased runoff and 

accretion . . . along the drain and further downstream in Auvase Creek.” Id. And it observed that 

increased runoff from the site would likely cause downstream areas to “see an increase in 

possible flooding magnitude and frequency.” Id. Justice Kennedy expressed concern that the 
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“conditional language in these assessments—‘potential ability,’ ‘possible flooding’—could 

suggest an undue degree of speculation.” Id.

Justice Kennedy’s observations regarding the above case provide guidance as to what it 

means for a nexus to be more than merely speculative or insubstantial and inform the proposed

definition of “significant nexus.” It is important to note, however, that where Justice Kennedy 

viewed the language “more than speculative or insubstantial” to suggest an undue degree of 

speculation, scientists do not equate certain conditional language (such as “may” or “could”) 

with speculation, but rather with the rigorous and precise language of science necessary when 

applying specific findings in another individual situation or more broadly across a variety of 

situations. Certain terms used in a scientific context do not have the same implications that they 

have in a legal or policy context. Scientists use cautionary language, such as “may” or “could,” 

when applying specific findings on a broader scale to avoid the appearance of overstating their 

research results and to avoid inserting bias into their findings (such that the reader may think the 

results of one study are applicable in all related studies). Words like “potential” are commonly 

used in the biological sciences, but when viewed under a legal and policy veil, may seem to 

mean the same as “speculative” or “insubstantial.” Instead, potential in scientific terms means 

ability or capability. For example, when the term “potential” is used to describe how a wetland 

has the potential to act as a sink for floodwater and pollutants, scientists mean that wetlands in 

general do indeed perform those functions, but whether a particular wetland performs that 

function is dependent upon the circumstances that would create conditions for floodwater or 

pollutants in the watershed to reach that particular wetland to retain and transform. That does not 

mean, however, that this nexus to downstream waters is “speculative;” indeed the wetland would 

be expected to provide these functions under the proper circumstances. 
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Clean Water Protection Rule

List of Subjects

33 CFR Part 328.3(a)

Administrative practice and procedure, Intergovernmental relations, Environmental 

protection, Navigation, Water pollution control, Waterways.

40 CFR Part 110.1

Environmental Protection, Water pollution control

40 CFR Part 112.2

Environmental Protection, Water pollution control

40 CFR Part 116.3

Environmental Protection, Water pollution control

40 CFR Part 117.1

Environmental Protection, Water pollution control

40 CFR Part 122.2

Environmental Protection, Water pollution control

40 CFR Part 230.2(s)

Environmental Protection, Water pollution control

40 CFR Part 232.2

Environmental Protection, Water pollution control

40 CFR Part 300.5

Environmental Protection, Water pollution control

40 CFR Part 300 App. E
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Environmental Protection, Water pollution control

40 CFR Part 302.3 

Environmental Protection, Water pollution control

40 CFR Part 401.11

Environmental Protection, Water pollution control

Dated: Dated:

Gina McCarthy, Jo Ellen Darcy,

Administrator Assistant Secretary of the Army

Environmental Protection Agency (Civil Works)

Department of the Army
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Proposed Rule

The following text replaces the text at 33 C.F.R. § 328.3(a), (b) and (c). 

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−
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(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 
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(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.
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(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. § 110.1:

Navigable waters means the waters of the United States, including the territorial seas. 

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;
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(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 
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groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 
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of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 
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sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. §112.2. 

Navigable waters means the waters of the United States, including the territorial seas. 

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 
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(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 
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(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 
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Page 292 of 325

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. §116.3. 

Navigable waters is defined in section 502(7) of the Act to mean ‘‘waters of the United States, 

including the territorial seas.”

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:
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(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 
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Page 294 of 325

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 
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(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 
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similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. §117.1(i). 

(i) Navigable waters means ‘‘waters of the United States, including the territorial seas.’’

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 
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(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 
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(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 
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break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “Waters of the United States” at 40 C.F.R. 

§122.2:

Waters of the United States or waters of the U.S. means:
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Page 300 of 325

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. This exclusion applies only to manmade bodies of water 

which neither were originally created in waters of the United States (such as disposal area in 
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Page 301 of 325

wetlands) nor resulted from the impoundment of waters of the United States. [See Note 1 of this 

section.] 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,
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Page 302 of 325

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 
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Page 303 of 325

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the text at 40 C.F.R. § 230.3(s) and (t). 

(s) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (t) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;
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(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(t) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 
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Page 305 of 325

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (s)(1) through (s)(3) of this section.

 

(u) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(s)(1) through (s)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 
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Page 306 of 325

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (s)(1) through (s)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (s)(1) through (s)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (s)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (s)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 
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Page 307 of 325

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (s)(1) through (s)(3) of this section. 

The following text replaces the definition of “Waters of the United States” at 40 C.F.R. 

§232.2:

Waters of the United States or waters means:

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 
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Page 308 of 325

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−
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Page 309 of 325

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 310 of 325

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. §300.5:

Navigable waters as defined by 40 CFR 110.1, means the waters of the United States, including 

the territorial seas.
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Page 311 of 325

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 312 of 325

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 313 of 325

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 314 of 325

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. § 300, 

Appendix E to Part 300, 1.5:

Navigable waters as defined by 40 CFR 110.1, means the waters of the United States, including 

the territorial seas.

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 315 of 325

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 316 of 325

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 317 of 325

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 318 of 325

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. § 302.3:

Navigable waters means the waters of the United States, including the territorial seas.

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 319 of 325

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry 

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles;

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 320 of 325

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 321 of 325

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section. 

The following text replaces the definition of “navigable waters” at 40 C.F.R. § 401.11:

(l) The term navigable waters means the waters of the United States, including the territorial 

seas.

(a) For purposes of all sections of the Clean Water Act, 33 U.S.C. 1251 et. seq. and its 

implementing regulations, subject to the exclusions in subsection (b) of this section, the term 

“waters of the United States” means:
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 322 of 325

(1) All waters which are currently used, were used in the past, or may be susceptible to use in 

interstate or foreign commerce, including all waters which are subject to the ebb and flow of the 

tide;

(2) All interstate waters, including interstate wetlands;

(3) The territorial seas;

(4) All impoundments of waters otherwise defined as waters of the United States under this 

definition;

(5) All tributaries of waters identified in paragraphs (1) through (3) of this section;

(6) All waters, including wetlands, adjacent to a water identified in paragraphs (1) through 

(5) of this section; and 

(7) On a case-specific basis, other waters, including wetlands, provided that those waters 

alone, or in combination with other similarly situated waters, including wetlands, located in the 

same region, have a significant nexus to a water identified in paragraphs (1) through (3) of this 

section. 

(b) The following are not “waters of the United States” −−

(1) Waste treatment systems, including treatment ponds or lagoons, designed to meet the 

requirements of the Clean Water Act. 

(2) Prior converted cropland. Notwithstanding the determination of an area’s status as 

prior converted cropland by any other federal agency, for the purposes of the Clean Water Act, 

the final authority regarding Clean Water Act jurisdiction remains with EPA; and,

(3) Artificially irrigated areas that would revert to upland should application of irrigation 

water to that area cease; artificial lakes or ponds created by excavating and/or diking dry land 

and used exclusively for such purposes as stock watering, irrigation, settling basins, or rice 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 323 of 325

growing; artificial reflecting pools or swimming pools created by excavating and/or diking dry

land; small ornamental waters created by excavating and/or diking dry land for primarily 

aesthetic reasons; water-filled depressions created incidental to construction activity; 

groundwater drained through subsurface drainage systems; gullies and rills; non-wetland swales; 

and puddles; 

(4) Ditches that are excavated wholly in uplands, drain only uplands or non-jurisdictional 

waters, and have no more than ephemeral flow; and 

(5) Ditches that do not contribute flow, either directly or through other waterbodies, to a 

water identified in paragraphs (a)(1) through (a)(3) of this section.

 

(c) Definitions −−

(1) Adjacent: The term adjacent means bordering, contiguous or neighboring. Waters, 

including wetlands, separated from other waters of the United States by man-made dikes or 

barriers, natural river berms, beach dunes and the like are “adjacent waters.” 

(2) Neighboring: The term neighboring, for purposes of the term “adjacent” in this section,

includes waters located within the riparian area or floodplain of a water identified in paragraphs 

(a)(1) through (a)(5) of this section, or waters with a surface or shallow subsurface hydrologic 

connection to such a jurisdictional water. 

(3) Riparian area: The term riparian area means an area bordering a water where surface or 

subsurface hydrology influence the ecological processes and plant and animal community 

structure in that area. Riparian areas are transitional areas between aquatic and terrestrial 

ecosystems that influence the exchange of energy and materials between those ecosystems. 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 324 of 325

(4) Floodplain: The term floodplain means an area bordering inland or coastal waters that was 

formed by sediment deposition from such water under present climatic conditions and is 

inundated during periods of moderate to high water flows. 

(5) Tributary: The term tributary means a waterbody physically characterized by the presence 

of a bed and banks and ordinary high water mark, which contributes flow, either directly or 

through other waterbodies, to a water identified in paragraphs (a)(1) through (a)(3) of this 

section. A waterbody that otherwise qualifies as a tributary under this definition does not lose its 

status as a tributary if, for any length, there are one or more man-made breaks (such as bridges, 

culverts, pipes, or dams), or one or more natural breaks (such as wetlands at the head of or along 

the run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a 

bed and banks and an ordinary high water mark can be identified upstream or downstream of the 

break. In addition, wetlands are tributaries (even if they lack a bed and banks and ordinary high 

water mark) if they contribute flow, either directly or through other waterbodies to a water 

identified in paragraphs (a)(1) through (a)(3) of this section. A tributary, including wetlands, can 

be a natural, man-altered, or man-made water body and includes waters such as rivers, streams, 

lakes, impoundments, canals, and ditches not excluded in paragraph (b)(4) and (b)(5) of this 

section.

(6) Wetlands: The term wetlands means those areas that are inundated or saturated by surface 

or groundwater at a frequency and duration sufficient to support, and that under normal 

circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, marshes, bogs and similar areas.

(7) Significant nexus: The term significant nexus means a more than speculative or 

insubstantial effect that a water, including wetlands, either alone or in combination with other 
*** E.O. 12866 Review – Draft – Do Not Cite, Quote, or Release During Review*** 

Page 325 of 325

similarly situated waters in the region (i.e., the watershed that drains to a water identified in 

paragraphs (a)(1) through (3) of this section), has on the chemical, physical or biological 

integrity of a water identified in paragraphs (a)(1) through (3) of this section. Other waters, 

including wetlands, are similarly situated when they perform similar functions and are located 

sufficiently close together or close to a “water of the U.S.” so that they can be evaluated as a 

single landscape unit with regard to their effect on the chemical, physical, or biological integrity 

of a water identified in paragraphs (a)(1) through (a)(3) of this section.