I n 2006, the Supreme Court decided Rapanos v. United States, the most recent and well-known of three Supreme Court decisions wrestling with the question of which wetlands are covered by the wetlands permitting program in the Clean Water Act (CWA). Since then, numerous decisions from the lower federal courts have sought to divine what criteria to draw from the fractured opinions in Rapanos as to which wetlands are "jurisdictional" (within the CWA's reach), and which are not. At the same time, the agencies charged with administering the wetlands permitting program, the U.S. Army Corps of Engineers and Environmental Protection Agency (EPA), issued several guidance documents seeking to explain their view of their +regulations that define "waters of the United States" for purposes of determining CWA jurisdictional waters. In 2015 the agencies issued revised regulations intended to clarify the scope of waters protected under the CWA. This report provides background including the pre- Rapanos Supreme Court opinions, then moves on to Rapanos itself and the Corps/EPA guidance documents. The 2015 rule is discussed briefly; it also is discussed in a separate CRS report (CRS Report R43455, EPA and the Army Corps' Rule to Define "Waters of the United States" , by [author name scrubbed]) . From the earliest days, Congress has grappled with where to set the line between federal and state authority over the nation's waterways. Typically, this debate occurred in the context of federal legislation restricting uses of waterways that impaired navigation and commerce. The phrase Congress often used to specify waterways over which the federal government had authority was "navigable waters of the United States." This "navigable waters" concept proved an elastic one: in Supreme Court decisions from the early to mid-20 th century, "navigability" underwent a substantial expansion "from waters in actual use to those which used to be navigable to those which by reasonable improvements could be made navigable to nonnavigable tributaries affecting navigable streams." Notwithstanding the Court's enlargement of "navigability," Congress considering the legislation that became the CWA of 1972 felt that the term was too constricted to define the reach of a law whose purpose was not maintaining navigability, as in the past, but rather preventing pollution. Accordingly, Congress in the CWA retained the traditional term "navigable waters," but defined it to mean "waters of the United States" —seemingly minimizing the constraint of navigability. The conference report said that the new phrase was intended to be given "the broadest possible constitutional interpretation." Among the provisions in the 1972 clean water legislation was Section 404, which together with Section 301(a) requires persons wishing to discharge dredged or fill material into "navigable waters," as newly defined, to obtain a permit from the U.S. Army Corps of Engineers. The Corps' initial response to Section 404 was to apply it solely to waters traditionally deemed navigable (which included few wetland areas), despite the broadening "waters of the United States" definition and conference report language. Under a 1975 court order, however, the Corps issued new regulations that swept in a range of wetlands. This broadening ushered in a debate, continuing today, as to which wetlands Congress meant to reach in the Section 404 permit program. At one time or another, the debate has occupied all three branches of the federal government. Wetlands, with a variety of physical characteristics, are found throughout the country. They are known in different regions as swamps, marshes, fens, potholes, playa lakes, or bogs. Although these places can differ greatly, they all have distinctive vegetative assemblages because of the wetness of the soil. Some wetland areas may be continuously inundated by water, while other areas may not be flooded at all. In coastal areas, flooding may occur on a daily basis as tides rise and fall. The Supreme Court's first foray into the Section 404 jurisdictional quagmire came in 1985, in Riverside Bayview Homes, Inc. v. United States. There, the Court unanimously upheld as reasonable the Corps' extension of its Section 404 jurisdiction to "adjacent wetlands"—as one component of the agency's definition of "waters of the United States." Under the Corps regulations, adjacent wetlands are wetlands adjacent to any non-wetland waterbody that constitutes a water of the United States—such as navigable bodies of water or interstate waters, or their tributaries. The Court reasoned that the water-quality objectives of the CWA were broad and sensitive to the fact that water moves in hydrologic cycles. Due to the frequent difficulties in defining where water ends and land begins, the Court could not say that the Corps' conclusion that adjacent wetlands are inseparably bound up with "waters of the United States" was unreasonable, particularly given the deference owed by courts to the Corps' and EPA's ecological expertise. Also persuasive was the fact that in considering the 1977 amendments to the CWA, Congress vigorously debated but ultimately rejected amendments that would have narrowed the Corps' asserted jurisdiction under Section 404. In 2001, the Court returned to the geographic reach of Section 404. The decision in Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers ( SWANCC ) directly involved the "isolated waters" component of the Corps' definition of "waters of the United States," rather than the "adjacent wetlands" component at issue in Riverside Bayview Homes . "Isolated waters," in CWA parlance (the regulations do not actually use the phrase), are waters that are not traditional navigable waters, are not interstate, are not tributaries of the foregoing, and are not hydrologically connected to navigable or interstate waters or their tributaries—but whose "use, degradation, or destruction [nonetheless] could affect interstate commerce." Illustrative examples listed in the regulations include "intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands , sloughs, [or] prairie potholes" with an interstate commerce nexus, or connection. The issue before the Court was whether "waters of the United States" is broad enough to embrace the Corps' assertion of jurisdiction over such "isolated waters" purely on the ground that they are or might be used by migratory birds that cross state lines—known as the Migratory Bird Rule. In a 5-4 ruling, the Court held that the Migratory Bird Rule was not authorized by the CWA. The decision's rationale was much broader, however, appearing to preclude federal assertion of 404 jurisdiction over isolated, nonnavigable, intrastate waters on any basis—indeed, over wetlands not adjacent to "open water." This disparity between the Court's holding and its rationale occasioned considerable litigation in the lower courts, the majority of which opted for a narrow reading of SWANCC , hence a broad reading of remaining Corps jurisdiction under Section 404. Such uncertainties as to the Corps' isolated waters jurisdiction after SWANCC focused attention on the alternative bases in Corps regulations for asserting 404 jurisdiction—such as the existence of "adjacent wetlands." Neither the Corps of Engineers nor EPA, however, has modified its Section 404 regulations since SWANCC . The new spotlight on the concept of "adjacent wetlands" became the backdrop for the Supreme Court's Rapanos decision, the Court's second encounter with this phrase after Riverside Bayview Homes. Rapanos was actually a consolidation of two cases, Rapanos and Carabell , on appeal from the Sixth Circuit. Though both cases involved issues as to what constitutes "adjacent wetlands," the issues in each are different. Rapano s in the Sixth Circuit involved the Corps' assertion of 404 jurisdiction over a wetland adjacent to a tributary (man-made ditch) that ultimately flowed, miles later, into a traditional navigable water. As in Riverside Bayview , the issue was the Corps' jurisdiction under the "adjacent wetlands" component of its regulations defining "waters of the United States." In particular, plaintiffs argued that SWANCC did more than throw out the Migratory Bird Rule; it also barred Section 404 regulation of wetlands that do not physically abut a traditional navigable water. In ruling that Section 404 reached the Rapanos's wetlands, the Sixth Circuit held that immediate adjacency of the wetland to a traditional navigable water is not required. Rather, what is needed is a "significant nexus"—a ubiquitous phrase in Section 404 court decisions lifted from SWANCC 's explanation of Riverside Bayview —between the wetlands and traditional navigable waters. "Significant nexus," in turn, can be satisfied by the presence of a "hydrological connection." Thus, the fact that the Rapanos's wetlands had surface water connections to nearby tributaries of traditional navigable waters was sufficient for Section 404 jurisdiction. Nor did it seem to matter to the court that the hydrological connection to traditional navigable waters was, for at least one of the Rapanos wetlands, distant—surface waters from this wetland flow into a man-made drain immediately north of the site, which empties into a creek, which flows into a navigable river. According to the record, this wetland is between 11 and 20 miles from the nearest navigable-in-fact water. In ruling that a surface water connection to a tributary of a navigable water was enough, the circuit aligned itself with the large majority of appellate courts to rule on this issue since SWANCC . In its petition for certiorari to the Supreme Court, the Rapanoses asked whether the CWA's reach extends to nonnavigable wetlands "that do not even abut a navigable water." Carabell in the Sixth Circuit involved the Corps' assertion of jurisdiction over a wetland adjacent to a tributary (man-made ditch) that ultimately flowed into traditional navigable waters—but the wetland was separated from the tributary by a manmade berm. The Sixth Circuit held that "adjacent wetlands" jurisdiction existed under the Corps regulations, even though the wetland was separated from a tributary of "waters of the United States" by a four-foot-wide manmade berm that blocked immediate drainage of surface water from the parcel to the tributary. The existence of the berm meant, critically, that unlike the wetlands in Rapanos , the wetlands here lacked any hydrological connection to navigable waters at all . Parenthetically, the fact that the "tributary" was merely a man-made ditch (which emptied into a creek, which flowed into a navigable lake) did not appear to be an issue in the case, as it was in Rapanos . Finally, the court endorsed the view of the majority of courts addressing the question that SWANCC spoke only to the Corps' "isolated waters" jurisdiction; it did not narrow the agency's "adjacent wetlands" authority involved here and broadly construed in Riverside Bayview . In its petition for certiorari, the Carabells asked whether Section 404 extends to "wetlands that are hydrologically isolated from any of the 'waters of the United States.'" For many who had waited so long to have "waters of the United States" clarified, the Rapanos decision (addressing the Sixth Circuit decisions in both Rapanos and Carabell ) was a disappointment. In three major opinions, the Court split 4-1-4 as to whether the Corps' assertions of 404 jurisdiction in the two cases before it comported with the CWA—that is, involved "waters of the United States." Justice Scalia wrote a four-Justice plurality opinion, ruling that the Corps had overreached and thus the Sixth Circuit decisions must be vacated and remanded for further proceedings applying the plurality's rule. Justice Kennedy, in a lone concurrence, also disagreed with the Corps' interpretation of the CWA, but would have applied a different approach than the plurality. He supplied the fifth vote supporting the vacation and remand, making that the judgment of the Court. (Five votes is a majority on the Supreme Court.) Finally, Justice Stevens wrote a four-Justice dissent upholding the Corps' reading of its jurisdiction. Accordingly, he would have affirmed the decisions below. The problem is that no single rationale in these three opinions commands the support of a majority of the Justices. Thus, lower courts addressing challenges to Corps 404 jurisdiction since Rapanos have struggled with what rule of decision to extract from the decision. Does the Scalia plurality decision control? Or does the Kennedy concurrence provide the test? Or is satisfying either of these adequate to support jurisdiction? Justice Scalia's plurality opinion asserts what is probably the narrowest view of 404 jurisdiction in the three major opinions, at least in most circumstances. His opening paragraphs set the tone by describing the substantial costs of applying for 404 permits, and the "immense expansion of federal regulation of land use that has occurred under the Clean Water Act." This critical tone continues with the opinion's description of how the lower courts, "[e]ven after SWANCC ," have continued to uphold the "sweeping" assertions of jurisdiction by the Corps over tributaries and adjacent wetlands. Justice Scalia goes on to construe "waters" in "waters of the United States" to mean only relatively permanent, standing or flowing bodies of water , such as streams, rivers, lakes, and other bodies of water "forming geographic features." This definition leads him to exclude "channels containing merely intermittent or ephemeral flow." Wetlands, our topic here, are included as "waters of the United States"—that is, are "adjacent" in the Corps' language—only when they have a "continuous surface connection" to bodies that are "waters of the United States" in their own right. By contrast, wetlands with only an intermittent, physically remote hydrological connection to "waters of the United States" are not covered by Section 404, according to the Scalia opinion. Importantly, the plurality sought to calm concerns that a narrow reading of Section 404 would eviscerate other sections of the CWA, particularly the point-source permitting program under Section 402 that is the heart of the act. That section, the plurality explained, does not require that the point source discharge directly into a jurisdictional water. It is enough that the discharged pollutant is likely to ultimately be carried downstream to such a jurisdictional water. Thus, unlike with Section 404, discharges into non-covered waters could still be regulated. Justice Kennedy's concurring opinion , in contrast to the absolute rules proposed by the plurality, offers a case-by-case test. He picks up on the "significant nexus" test used by the Sixth Circuit and many other courts—but while the lower courts defined significant nexus as having a hydrological connection with traditional navigable waters, Justice Kennedy used an ambiguous ecological test. A wetland, he declared, has the requisite significant nexus if, alone or in combination with similarly situated lands in the region, it significantly affects the chemical, physical, and biological integrity of traditional navigable waters. These ecological functions include flood retention, pollutant trapping, and filtration. Under Kennedy's opinion, the waters that perform these functions may be intermittent or ephemeral, and they need not have a surface hydrological connection to other waters. When, in contrast, their effects on water quality are speculative or insubstantial, the wetland is beyond Section 404's reach. This formulation, Justice Kennedy explained, allows that when the Corps seeks to regulate wetlands adjacent to navigable-in-fact waters, adjacency is enough for jurisdiction. In contrast, for wetlands sought to be regulated based on adjacency to non-navigable tributaries , a significant nexus must be shown on a case-by-case basis. Importantly, however, the Justice did allow that the Corps might adopt regulations at some point declaring certain categories of wetlands to have a significant nexus per se, obviating the case-by-case approach for those wetlands. Each of the foregoing views—the plurality's and Justice Kennedy's—rejects the hitherto prevailing view that any hydrological connection to a traditionally navigable water, no matter how distant, is sufficient for coverage. This "any hydrological connection" test had been a key element of the United States' assertions of "adjacent wetlands" jurisdiction. The four dissenters found the Corps' assertion of jurisdiction reasonable in both cases. The Court's earlier decision in Riverside Bayview , the dissenters argued, was not confined to wetlands having continuous surface flow with traditional navigable waters or their tributaries. Rather it had endorsed jurisdiction over non-isolated wetlands generally, without case-by-case analysis. The plurality's concerns about the costs of applying for a permit, they continued, are more properly addressed to Congress, not to a court. The jurisdictional questions raised by Rapanos and Carabell presented the Supreme Court with a "perfect storm" of hot-button issues. First, there is the federalism matter: Where do CWA Section 404 and the Constitution's Commerce Clause draw the line between federal and state authority over wetlands? Second, there are property rights concerns. Some 75% of jurisdictional wetlands in the lower 48 states are on private property, with the result that protests from property owners denied Section 404 permits (or subjected to unacceptable conditions on same) are often heard, sometimes in the courts through Fifth Amendment takings suits. Third, Rapanos and Carabell have pervasive significance within the CWA itself, since "waters of the United States" governs not only the Section 404 wetlands permitting program, but also multiple other provisions and requirements of that law (see discussion below under " Policy Implications "). In addition, the Corps' broad reading of its jurisdiction created novel semantics (such as viewing dry arroyos as "waters," and manmade ditches as "tributaries") that Justices inclined to more literal readings of statutory language would have a hard time accepting. It was not surprising in light of the above themes that the Justices split as they did: the four more "conservative" Justices rejecting the Corps' expansive view of its adjacent wetland jurisdiction, the four "liberal/moderates" upholding it, and Justice Kennedy coming down in between (as he often does) with a case-by-case test, at least until the Corps adopts new rules. The question, as noted earlier, is what rule of decision the lower courts will discern in Rapanos , with its absence of a majority rationale, for use in future cases. In practice, courts often look for common approaches supported by a majority of the Justices, looking both to the views of plurality Justices (supporting the judgment of the court in the case) and those of the dissenters (who do not support the judgment). Thus far, lower courts applying Rapanos have drawn different tests from the decision, as was predicted based on its fractured nature. Nine of the thirteen federal circuits have ruled so far, an indication of the frequency with which CWA jurisdictional questions arise. Two federal circuits held that the Kennedy "significant nexus" test alone controls; two applied the Kennedy test but reserved for another day the question whether the plurality test as well is valid; three accepted Justice Stevens's suggestion that a wetland satisfying either the Kennedy or plurality tests is jurisdictional; and two avoided the issue altogether by finding that the Kennedy test and plurality test were both satisfied by the particular wetland in the case. (See Figure A-1 in the Appendix to this report.) No circuit decision has opted for the plurality test alone. As the footnotes below show, the Supreme Court has declined to review every one of these circuit decisions where a petition for certiorari has been filed. The likely reason for these consistent denials is that with no change in the Justices since Rapanos that is likely to make a difference in their voting pattern, the Court may see little point to taking another case in the area. District court decisions, at least the reported ones, seem to all follow either the Kennedy test alone or the Kennedy-or-plurality test view. As with the appellate decisions, there appears to be no reported district-court decision squarely holding that the plurality test alone governs. To a considerable extent, the court decisions turn on how the courts read Supreme Court guidance on what rule of law may be inferred from decisions of the Court in which no rationale commands the support of five or more Justices. The United States, for its part, has consistently taken the Kennedy-or-plurality position in litigation, as it did in congressional testimony soon after the Rapanos decision and in the Corps/EPA guidance on interpreting Rapanos (discussed below). In the wake of Rapanos , several factors arguably put pressure on the Corps and EPA to do a rulemaking on the scope of "adjacent wetlands" permitting jurisdiction under the CWA (assuming Congress does not act). One is the fact that no fewer than three of the opinions in Rapanos urged the agencies to do so. A second factor is the labor-intensive nature (and vagueness) of the Kennedy case-by-case approach, requiring empirical study of each wetland near a non-navigable tributary. The third factor is the divergence of the lower courts as to the rule to be applied after Rapanos . One can be confident, however, that anything the Corps and EPA promulgate will find its way into the courts. The agencies stated in guidance issued in 2008 that "further consideration of jurisdictional issues, including clarification and definition of key terminology, may be appropriate in the future, either through issuance of additional guidance or through rulemaking." All of the Rapanos opinions that mention SWANCC seem to accept, without discussion, that SWANCC eliminates jurisdictional coverage of all isolated, intrastate, nonnavigable waters—not just those isolated, intrastate, nonnavigable waters where the sole basis for asserting jurisdiction was the Migratory Bird Rule. Most lower court decisions to broach this issue had adopted the latter narrower reading of SWANCC . Thus, although only adjacent wetlands were directly involved in Rapanos , there may be impacts on the Corps' authority over isolated, intrastate, nonnavigable waters also. Finally, although both petitions for certiorari in Rapanos raised the Commerce Clause issue, the decision in Rapanos , as expected, was on purely statutory grounds. The plurality, however, did assert that the Corps view of its adjacent wetlands jurisdiction "stretches the outer limits of Congress' commerce power," using this as one of several reasons for adopting a narrow reading of that jurisdiction. This plurality view is plainly relevant to congressional bills seeking to overturn SWANCC and Rapanos by amending the CWA to explicitly assert jurisdiction over waters to the fullest extent consistent with the Constitution (see " Legislative Consideration "). In December 2008, EPA and the Corps of Engineers issued guidance to their field offices on how Rapanos should be interpreted in jurisdictional determinations, agency enforcement actions, and other agency actions. The guidance does not impose legally binding requirements on EPA or the Corps, and may not apply in a particular circumstance. The Corps and EPA had previously issued other guidance, attempting to clarify the Court's rulings on the jurisdictional issues discussed here. Following the Rapanos ruling, the agencies first issued informal guidance in 2006; it was replaced by formal guidance in June 2007. The December 2008 guidance made limited changes to the 2007 guidance and supersedes it. The 2008 revisions were made after review of public comments on the 2007 guidance and evaluation of the agencies' own implementation of the guidance. However, they noted in 2008, "The agencies will continue to monitor implementation of the Rapanos Guidance and, as we gain experience, consider appropriate opportunities to provide additional guidance or to initiate rulemaking." This statement encouraged those who argue that revised regulations are needed to resolve lingering interpretive questions. Others contend that a legislative remedy is required. The 2008 guidance generally adopts the Kennedy-test-or-plurality-test view, with the addition of agency interpretation of vague phrases in the Kennedy and plurality opinions. It has three parts, addressing waters that are (1) categorically within the scope of "waters of the United States"; (2) within "waters of the United States" or not, to be evaluated on a case-by-case basis; or (3) categorically outside the scope of "waters of the United States." (1) Waters categorically labeled "waters of the United States"—that is, without a case-by-case inquiry into whether there is a "significant nexus" with a traditional navigable water—are first, traditional navigable waters and their adjacent wetlands. Under this test, the existence of a continuous surface connection, as demanded by the plurality, but not Kennedy or the dissenters, is required to establish adjacency. Categorical "waters of the United States" also include non-navigable tributaries of traditional navigable waters, where such tributaries are "relatively permanent waters" (i.e., typically flowing year-round or at least seasonally) and adjacent wetlands with a continuous surface connection to such tributaries (not separated by uplands, berms, etc.). The 2008 guidance states that a wetland is adjacent if it has an unbroken hydrologic connection to jurisdictional waters, or is separated from those waters by a berm or similar feature, or if it is in reasonably close proximity to a jurisdictional water. (2) Waterbodies that are "waters of the United States" on a case-by-case basis are those dependent on a finding of a "significant nexus" with a traditional navigable water, per the Kennedy concurrence. They include non-navigable tributaries that are not relatively permanent (such as intermittent and ephemeral streams) and their adjacent wetlands, and wetlands adjacent to but that do not directly abut a relatively permanent non-navigable tributary. The 2008 guidance states that, in making the site- and fact-specific analysis to determine "significant nexus," the agencies will evaluate hydrology (e.g., proximity to traditional navigable waters), ecologic factors (e.g., ability of wetlands to trap and filter pollutants or store flood waters), and flow characteristics (flow and functions of the tributary and adjacent wetlands). The purpose of these tests is to demonstrate a connection and the role of a tributary and any adjacent wetlands in protecting the chemical, physical, and biological integrity of downstream traditional navigable waters. (3) Waterbodies not generally considered "waters of the United States" are swales or erosional features (e.g., gullies) and ditches (including roadside ditches) excavated wholly in and draining only uplands, and that do not carry a relatively permanent flow of water. The agencies generally will not assert jurisdiction over these waterbodies. To provide greater transparency of decisionmaking, the 2007 guidance required the Corps and EPA to be more thorough in documenting their jurisdictional determinations than in the past. To meet this requirement, which continues under the 2008 guidance, the Corps uses a standardized documentation form and posts results on its District websites. These steps respond to criticism, such as detailed in a GAO report, that Corps district offices have used differing practices in making jurisdictional determinations and that few districts made their documentation public. Overall, stakeholder groups, including industry, environmental advocates, and states, expressed disappointment or frustration with the 2007 guidance and the 2008 revision—some believing that it goes too far in narrowing protection of wetlands and U.S. waters, others believing that it does not go far enough. Generally, most agree that implementing the "significant nexus" test is especially difficult, because the guidance is complicated and vague. Industry groups said that because there are no clear guideposts on this key point, the guidance fails to provide the certainty desired by the regulated community. Environmentalists said that the "significant nexus" test in the guidance is more limited than the standard described by Justice Kennedy, because although his opinion recognizes the impact of losing wetlands or other small tributaries on large waters, the guidance does not account for cumulative effects. In evaluating "significant nexus," the guidance focuses only on a tributary and wetlands adjacent to that tributary. The 2008 revised guidance did not modify the 2007 guidance with respect to evaluating "significant nexus." Overall, industry groups reportedly believe that the 2008 revisions provided modest improvement over the earlier guidance and could make some jurisdictional determinations easier, but environmental advocates asserted that the guidance substantially limits waters protected by the CWA. One issue that has caused considerable confusion following the Rapanos ruling concerns CWA jurisdiction over wetlands not immediately adjacent to traditional navigable waters—including how jurisdiction will be applied in states within the Fourth, Seventh, Ninth, and Eleventh Circuits, where appellate courts have subsequently said that the Kennedy test alone is controlling. As noted, the 2008 guidance adds some clarification about determining adjacency, but questions about this and other interpretive issues have continued to arise. Since the initial 2007 guidance was issued, the CWA permitting process has become more complex and is slower, according to many participants and observers. A revealing EPA memorandum in March 2008 reports that since July 2006 (shortly after Rapanos was decided), the Rapanos ruling or the 2007 guidance negatively affected approximately 500 enforcement cases, a "significant portion" of the CWA enforcement docket. The breakdown identified in the EPA memo is 304 instances in which EPA regions decided not to pursue formal enforcement because of jurisdictional uncertainty, 147 instances where the enforcement priority of a case was lowered due to jurisdictional concerns, and 61 cases where lack of CWA jurisdiction has been asserted as an affirmative defense in an enforcement case. The memorandum goes on to say the greatest burden on the government results from "the implied presumption of non-jurisdiction [in the plurality test] for the most common types of waters in our country, intermittent and ephemeral tributaries to traditionally navigable waters and headwater wetlands. This presumptive exclusion can only be overcome by a resource-intensive 'significant nexus analysis' [the Kennedy test] described in the Guidance." The memorandum recommended "a few targeted revisions" to the guidance that OECA believed would address these issues, while remaining consistent with the Rapanos decision. For example, it recommended revising the guidance to incorporate Justice Kennedy's suggestions that, when evaluating jurisdiction, it is appropriate to consider wetlands either alone or in combination with other similarly situated lands in the region. The 2008 revised guidance did not address this recommendation. Echoing the EPA memorandum, a Corps official stated at a 2008 conference that making jurisdictional determinations is 8 to 10 times more resource-intensive for Corps staff who must consider a multitude of factors to determine what constitutes a "significant nexus." Representatives of developers and environmental advocates concurred that the joint guidance exacerbates permitting delays. Concern about this reported impact on CWA enforcement drew the attention of two House committee chairmen in 2008. Their staffs reviewed a large number of EPA and Corps documents and concluded that there had been a significant decline in CWA inspections, investigations, and enforcement actions since the Rapanos ruling and the 2007 guidance. In 2009, the EPA Inspector General (IG) reported that Rapanos has created a lot of uncertainty regarding Corps permitting and EPA's compliance and enforcement activities, because of jurisdictional issues, extensive analytical and data needs in more instances, and difficulty in interpreting waters based on "isolation," "adjacency," "neighboring," and related key terms. The IG's report was based on interviews with EPA and Army Corps staff in Washington, DC, and regional offices. In 2011, the Obama Administration weighed into the CWA jurisdiction debate as EPA and the Corps proposed new joint agency guidance to clarify regulatory jurisdiction over U.S. waters and wetlands and to replace the agencies' 2003 and 2008 guidance. The proposed revisions were built on the existing guidance with modifications that the agencies believed were consistent with the CWA, the Court's rulings, and science. According to the agencies, the guidance was focused on protecting smaller waters that feed into larger ones, to keep downstream water safe from upstream pollutants. Like the 2008 guidance, the 2011 revisions proposed to adopt the Kennedy-test-or-plurality-test view of Rapanos . However, the agencies believed that a wider evaluation of jurisdiction is possible than the 2008 guidance suggests, stating, "after careful review of these opinions, the agencies concluded that previous guidance did not make full use of the authority provided by the CWA to include waters within the scope of the Act, as interpreted by the Court." EPA and the Corps acknowledged that, compared with the existing guidance, the proposed revisions were likely to increase the number of waters identified as protected by the CWA. EPA and Corps officials believed that the likely increase in jurisdictional waters would occur because, in their view, the existing guidance under-protects waters and has created uncertainty about many gray areas of jurisdiction, which the revised guidance was intended to clarify. Although there still would be need for case-by-case determination of "significant nexus" waters (i.e., to demonstrate potential hydrologic or ecological connections to jurisdictional waters), the proposed revisions were intended to make such evaluations clearer. Critical reaction to the proposed revisions began even before release of the document. Industry criticism focused on two issues: (1) the revised guidance would broaden the number and kinds of waters subject to regulation, in their view beyond what the CWA and the Supreme Court's rulings permit; and (2) government was attempting to effect policy change through non-binding guidance that generally is not reviewable by courts. EPA and Corps officials responded that the guidance would not extend federal protection to any waters not historically protected under the Clean Water Act and would be fully consistent with the law, including decisions of the Supreme Court. Most state and local officials were supportive of clarifying the scope of CWA-regulated waters, but some were concerned that expanding the CWA's scope could impose costs on states and localities as their own actions (e.g., transportation projects) become subject to new requirements. Environmental advocacy groups welcomed the new guidance. The proposed guidance drew congressional attention, as well, both before and after its release. Some Members wrote letters supporting issuance of new guidance to address the confusion resulting from the Supreme Court's rulings. Others criticized the revised guidance as going beyond clarification and thus amounting to a de facto rule, instead of advisory guidelines. Legislative provisions to prohibit the agencies from funding activities related to revising the guidance were included in several appropriations bills in the 112 th and 113 th Congresses, but none of these provisions was enacted. As noted, the uncertainties resulting from the Rapanos decision led to widespread anticipation that the Corps and EPA would take administrative action to clarify how they interpret the ruling and its impact on waters that are protected by the CWA. Corps and EPA officials testified before a Senate subcommittee in 2006 that the agencies were working on substantive interpretive guidance to clarify CWA jurisdiction in light of the decision —the guidance that was eventually released in 2007 and was revised in 2008. While most observers acknowledged that guidance was useful, many urged the Corps and EPA to initiate a rulemaking to revise their regulations—especially since three Justices in some fashion suggested doing so. This view is, in fact, widely held by many diverse stakeholders—environmental groups, industry, and states—who, at the same time, disagreed on the substance of regulatory or other changes. Because the 2011 proposed guidance was not finalized (it was withdrawn from interagency review in September 2013), the existing 2003 and 2008 guidance remained in effect. However, in May 2015, EPA and the Corps jointly announced a rule to revise regulations that define "waters of the United States," that is, waters protected under the CWA. The revised rule would replace the SWANCC and Rapanos guidance and existing EPA-Corps rules. According to the agencies, the new rule—which they now refer to as the Clean Water Rule—revises the existing administrative definition of "waters of the United States" in regulations consistent with legal rulings—especially the recent Supreme Court cases—and science concerning the interconnectedness of tributaries, wetlands, and other waters to downstream waters and effects of these connections on the chemical, physical, and biological integrity of downstream waters. The agencies assert that the rule also reflects their expertise and experience in administering the CWA, including making more than 120,000 case-specific jurisdictional determinations since 2008. The rule is particularly focused on clarifying the regulatory status of surface waters located in isolated places in a landscape (the types of waters with ambiguous jurisdictional status following the Supreme Court's 2001 ruling in SWANCC ) and small streams, rivers that flow for part of the year, and nearby wetlands (the types of waters affected by the Court's 2006 ruling in Rapanos ). In developing the rule, EPA and the Corps relied on a synthesis prepared by EPA's Office of Research and Development of more than 1,200 published and peer-reviewed scientific reports; the synthesis discusses the current scientific understanding of the connections or isolation of streams and wetlands relative to large water bodies such as rivers, lakes, estuaries, and oceans. The purpose of the scientific synthesis report was to summarize current understanding of these connections, the factors that influence them, and the mechanisms by which connected waters affect the function or condition of downstream waters. The document was reviewed by EPA's Science Advisory Board (SAB), which provides independent engineering and scientific advice to the agency and which completed its review in October 2014. The final rule retains much of the structure of the agencies' existing definition of "waters of the United States." Like the 2003 and 2008 guidance, it identifies categories of waters that are and are not jurisdictional, as well as categories of waters that require a case-specific evaluation. Overall, EPA and the Corps say that their intent in the Clean Water Rule was to clarify their jurisdiction, in light of the Supreme Court's ruling, not to expand it. The agencies acknowledge that the rule would increase the asserted geographic scope of CWA jurisdiction, when compared to a baseline of current practices under the previous regulations and guidance. They believe, however, that the rule does not protect any new types of waters that have not been protected historically (i.e., prior to the SWANCC and Rapanos rulings) or exceed the CWA's coverage. That is, while it would enlarge jurisdiction beyond that under the 2008 EPA/Corps guidance, which the agencies believe was narrower than is justified by science and the law, they believe that it would not enlarge jurisdiction beyond what is consistent with the Supreme Court's narrow reading of jurisdiction. The rule was controversial even before it was proposed in March 2014, and controversies have persisted since the final rule was issued, including among Members of Congress. Officials of the Corps and EPA have vigorously defended it. In changing the regulatory definition of "waters of the United States," there may be instances in which the CWA applies categorically for the first time, and there also may be instances in which the CWA no longer applies (i.e., as a result of exemptions and exclusions). The agencies intend that the rule will result in less ambiguity about whether the CWA applies than under existing regulations, legal rulings, and guidance. Industries that are the primary applicants for CWA permits and agriculture groups (although farms are exempt from most permitting) object to how broadly they fear that the rule will be interpreted and have been concerned that existing exemptions for agriculture, which the rule did not affect, would be modified. Some local governments raised concerns that the rule would increase the number of locally owned ditches under federal jurisdiction. Many states and state environmental agencies expressed support for a rule to clarify the scope of CWA jurisdiction, but there is no state consensus on the revised rule. Some are generally supportive, but others believe that the agencies did insufficient consultation with the states prior to proposing the rule. States, they point out, are co-regulators of the CWA with EPA, making questions of federal jurisdiction equally important to state interests. Environmental groups defend the agencies' efforts to protect U.S. waters and reduce frustration resulting from unclear jurisdiction of the CWA. Still, some of them argued that the proposed rule should have been strengthened, for example by designating additional categories of waters and wetlands such as prairie potholes as categorically jurisdictional. The final rule did not do so; instead, such waters will require case-specific analysis to determine if jurisdiction applies. New regulations may clarify many current questions, but they are unlikely to please all of the competing interests, as one environmental advocate observed. However, a rulemaking would only benefit wetlands if it did not reduce the jurisdiction offered by current regulations and if the Administration remained faithful to sound science. If politics were to trump science in the rulemaking process, the likelihood of such a protective rule would not be promising. Also, rules are subject to legal challenge and can be tied up in court for years before they are implemented. The revised rule became effective August 28, 2015. However, legal challenges to the Clean Water Rule were filed in multiple federal courts soon after it was announced. These lawsuits, filed by industry groups, more than half of the states, and several environmental groups (nearly 90 plaintiffs so far), will test whether the agencies' interpretation of CWA jurisdiction is consistent with the Supreme Court's rulings and whether the rule complies with substantive and procedural requirements of the CWA and other laws. Because of uncertainty about the correct judicial venue for challenging the rule, petitions for review have been filed both in federal district courts and courts of appeals. The petitions for review of the rule in courts of appeals have been consolidated in the U.S. Court of Appeals for the Sixth Circuit. On October 9, a three-judge panel of the Sixth Circuit placed a nationwide stay on the rule, pending further developments, including the need to determine the court's own jurisdictional authority. On February 22, 2016, the Sixth Circuit ruled that it had jurisdiction to hear consolidated challenges to the final rule. The central question before the court hinged on interpretation and application of the appellate judicial review provision of the CWA. The petitioners and intervenors challenging the rule had argued that the rule did not fall into the categories of actions described in the CWA for direct review in appellate courts, and therefore that the challenges to the rule should be heard in the district courts. The Sixth Circuit, in a 2-1 ruling, ultimately agreed with the federal government that the rule was reviewable exclusively in the circuit courts. Other legal complexities remain, however, including continuing district court cases over the rule in other circuits and a pending decision on the same issue in an appeal before the U.S. Court of Appeals for the Eleventh Circuit. As a result of the court's October 2015 order and February 22 ruling, the Corps and EPA will continue to make CWA jurisdictional determinations based on the 2008 guidance, as they did before promulgation of the 2015 rule. As with the legal questions, the policy questions associated with the Supreme Court cases—what should be the outer limit of CWA regulatory jurisdiction and what are the consequences of restricting that jurisdiction—also have challenged regulators, landowners and developers, and policymakers since passage of the act in 1972. The act prohibits the discharge of dredged or fill material into navigable waters without a permit, and it also prohibits discharges of pollutants from any point source to navigable waters without a permit. Disputes have centered on whether wetlands and other waters are "navigable waters," a legal term of art. The answer to this question is important, because it may determine the extent of federal CWA regulatory authority not only for the Section 404 program, but also for purposes of implementing other CWA programs. Critics of the Section 404 regulatory program, such as land developers and agriculture interests, argue that the Corps' wetlands program has gradually and illegally expanded its asserted jurisdiction since 1972. They want the Corps and EPA to give up jurisdiction over most non-navigable tributaries and allow other federal and state programs to fill whatever gap is created. Waters that are jurisdictional are subject to the multiple regulatory requirements of the CWA: standards, discharge limitations, permits, and enforcement. Non-jurisdictional waters, in contrast, do not have the federal legal protection of those requirements. The act has one definition of "navigable waters" that applies to the entire law. In particular, the definition applies to federal prohibition on discharges of pollutants (§301), requirements to obtain a permit prior to discharge (§§402 and 404), water quality standards and measures to attain them (§303), oil spill liability and oil spill prevention and control measures (§311), certification that federally permitted activities comply with state water quality standards (§401), and enforcement (§309). It impacts the Oil Pollution Act and other environmental laws, as well. For example, the reach of the Endangered Species Act (ESA) is affected, because of that act's requirement for consultation by federal agencies over impacts on threatened or endangered species is triggered through the issuance of federal permits. Thus, by removing the need for a CWA permit, a non-jurisdictional determination would eliminate ESA consultation, as well. As discussed above, the Scalia plurality opinion in Rapanos concluded that a narrow interpretation of the Corps' 404 jurisdiction would not impact these other provisions, but many observers contend that the question is not fully resolved. For example, a number of EPA regional staffers cited in a 2009 EPA Inspector General's report stated that some of the most challenging enforcement cases in the post- Rapanos world have involved non-404 issues. EPA said that it might issue additional guidance concerning the effect of Rapanos on other CWA programs that use the common "waters of the United States" definition, but it has not done so. In March 2008, EPA officials reportedly asked states to assist in developing guidance to govern CWA jurisdiction decisions under Section 402, because of continuing uncertainty on the law's scope, especially in western states that have a preponderance of intermittent and ephemeral streams. It is unclear whether this guidance was developed. SWANCC found invalid the assertion of CWA jurisdiction over isolated, non-navigable intrastate waters solely on the basis of their use (or potential use) as habitat by migratory birds. Most of the post- SWANCC cases have instead addressed tributaries and adjacent wetlands, asking which of these have the "significant nexus" to navigable waters that SWANCC was interpreted to say is necessary to establish federal jurisdiction. Wetlands are an important part of the total aquatic ecosystem, with many recognized functions and values, including water storage (mitigating the effects of floods and droughts), water purification and filtering, recreation, habitat for plants and animals, food production, and open space and aesthetic values. Functional values, both ecological and economic, at each wetland depend on its location, size, and relationship to adjacent land and water areas. To the layman, many of these values are more obvious for wetlands adjacent to large rivers and streams than they are for wetlands and small streams that are isolated in the landscape from other waters. Many of the functions and values of wetlands have been recognized only recently. Historically, many federal programs encouraged wetlands to be drained or altered because they were seen as having little value. Even today, while more federal laws either encourage wetland protection or regulate their modification, pressure exists to modify, drain, or develop wetlands for uses that some see as more economically beneficial. While regulators and the regulated community debate the legal dimensions of federal jurisdiction, scientists contend that there are no discrete, scientifically supportable boundaries or criteria along the continuum of waters/wetlands to separate them into meaningful ecological or hydrological compartments. Numerous scientific studies define and describe the importance of the functions and values of wetlands, in support of their significant nexus to navigable waters. In all but some very narrow instances, scientists say, terms such as "isolated waters" and "adjacent wetlands" are artificial legal or regulatory constructs, not valid scientific classifications. From this perspective, even waters and wetlands that lack a direct surface connection to navigable waters or that only flow intermittently are connected to the larger aquatic ecosystem via subsurface or overflow hydrologic connections. Wetland scientists believe that all such waters/wetlands are critical for protecting the integrity of waters, habitat, and wildlife downstream. In SWANCC , the Supreme Court did not draw a bright line for purposes of determining the limits of federal jurisdiction (many wetland scientists do not believe that a bright line is possible, in any case). While the ruling reduced federal jurisdiction over some previously regulated wetlands, even more than a decade later it remains difficult to determine the precise effect of that decision. Many affected interests (states and the regulated community) contend that the 2003 guidance from the Corps and EPA did not adequately define the scope of regulated areas and wetlands affected by SWANCC and subsequent court rulings. The Rapanoses and the Carabells had hoped that the Supreme Court would clarify the jurisdiction issue and that the Court would further narrow the program's geographic reach. Other interest groups disagreed with the petitioners' views on the issues, but also had hoped for clarity. Most say that the 4-1-4 ruling, in which the three main opinions did not agree on what constitutes "waters of the United States," did not bring the desired clarity of meaning in legal and policy terms. Estimates of the types of wetlands and amounts of acreage affected by SWANCC, Rapanos , and subsequent lower court rulings depend on interpretation of the cases and on assumptions about defining key terms such as "adjacent," "tributary," and "significant nexus." Because in its regulations before SWANCC the Corps had broadly defined "waters of the United States," including those encompassed by the Migratory Bird Rule, nearly all U.S. wetlands and waters were subject to CWA jurisdiction, since practically all are used to a greater or lesser extent by migratory birds. Depending on how key terms are defined, reduced federal jurisdiction could affect very small or very large categories of waters and wetlands. Reflecting the uncertainties about how broadly or narrowly SWANCC would be interpreted, one estimate made after that decision found that the possible changes in jurisdiction could range from 20% to 80% of the nation's total estimated 100 million acres of wetlands. Following the Rapanos decision, concern was expressed particularly about that ruling's impacts in arid and semi-arid western states to exclude intermittent or ephemeral streams and adjacent wetlands and riparian areas from CWA jurisdiction. A reduction in CWA jurisdiction affects implementation of the 404 and possibly other CWA programs. Early in 2006, EPA estimated conservatively that the extent of non-navigable tributaries and adjacent wetlands that could be affected by the narrow reading of the Clean Water Act that was advocated by the Rapanos and Carabell petitioners was up to 59% of the total length of streams in the United States, excluding Alaska. EPA also estimated that 34% of industrial and municipal dischargers that are subject to CWA Section 402 permits are located on these stream segments and that public drinking water systems which use intakes on these segments provide drinking water to over 110 million people. Because there is no national database of non-navigable tributaries, EPA analyzed surrogate data on the linear extent of intermittent/ephemeral streams and stream segments that lie at the head of tributary systems and have no other streams flowing into them. Some estimate that the smallest, or headwater, first- and second-order streams represent more than 75% of the nation's stream network and provide drinking water for 117 million people—one in three Americans. These streams, if left unprotected by expansive interpretation of the Court's rulings, are at risk from a variety of polluting activities due to urbanization, construction, and channelization for flood control purposes. Whatever gaps in wetland regulation result from reduced federal jurisdiction arguably could be filled, at least in part, by other federal or state and local programs and actions. For example, some assert that wetland restoration and creation programs, such as the Wetlands Reserve Program and the Coastal Wetlands Restoration Program, or private conservation efforts can provide protection, even if the wetland is no longer jurisdictional under federal law. However, others respond that such programs are likely to be incomplete in filling gaps, since they apply primarily to rural areas and do not apply to the one-third of the nation's lands in federal ownership. Moreover, they were never intended to be a seamless group that would fill all possible gaps. SWANCC, Rapanos , and the subsequent lower court decisions also highlight the role of states in protecting waters not addressed by federal law. From the states' perspective, the federal Section 404 program provides the basis for a consistent national approach to wetlands protection. But if a larger portion of wetlands are no longer federally jurisdictional, they say, it can be argued that the Section 404 program no longer provides a baseline for consistent, minimum standards to regulate wetlands. None of these court rulings prevents states from protecting non-jurisdictional waters through legislative or administrative action, but few states have done so. Prior to SWANCC , 15 states had programs that regulate isolated freshwater wetlands to some degree, but state officials acknowledge that these programs vary substantially from some that are comprehensive in scope to others that are limited by wetland size or have exemptions for agriculture and other activities. Since 2001, a few states have passed new legislation or updated water quality regulations; the issue remains under consideration in several states, where competing proposals that are viewed by some as strengthening and by others as weakening wetland protection have been debated. Critics of broad assertion of federal jurisdiction over water resources point out that most states have authorities to regulate waters of their state, often beyond the scope of federal jurisdiction. In some cases, however, their ability to regulate effectively may be compromised, because state rules often are tied to federal definitions. The gap produced by reduced federal jurisdiction is most evident in the 32 states that have no independent wetlands programs and that typically have relied on CWA Section 401 water quality certification procedures to protect wetlands. Pursuant to Section 401, applicants for a federal permit must obtain a state certification that the project will comply with state water quality standards. Consequently, by conditioning certification, states have the ability to affect the federal permit and to exercise some regulatory control over wetlands without the expense of establishing independent state programs. However, as described previously, diminished CWA jurisdiction which affects the Section 404 program also limits the reach of other CWA programs, including Section 401. Analysts familiar with the political and fiscal environments of states believe that most states are either reluctant or unable "to step boldly into the breach in federal wetlands protection.... The Corps and the U.S. Environmental Protection Agency, not to mention Congress, have little cause to rely on the notion that states will effectively backstop federal protection for isolated wetlands." Many states are barred from enacting laws more stringent than federal rules, or are reluctant to take action, due to budgetary and resource concerns, as well as apprehension that regulation will be judged to involve "taking" of private property and require compensation. Some argue that what is needed—regardless of interpretive guidance or rulemaking by the Corps and EPA—is legislative action to affirm Congress's intention regarding CWA jurisdiction. Others contend that, although the Rapanos decision did not resolve the issues, it also did not substantially affect Congress's willingness or interest in acting on issues that have been pending for several years without congressional action. Related to this is the view that, because the current questions are highly technical in nature, a simple fix may not address the problem, or may create others, such as impacting rights that the CWA reserves to states. In the 109 th Congress, bills were introduced to address the CWA jurisdictional issues in different ways, but Congress took no action. One proposal (the Clean Water Authority Restoration Act of 2005) would have provided a broad statutory definition of "waters of the United States"; would have clarified that the CWA is intended to protect U.S. waters from pollution, not just maintain their navigability; and would have included a set of findings to assert constitutional authority over waters and wetlands. Other legislation intended to restrict regulatory jurisdiction also was introduced (the Federal Wetlands Jurisdiction Act of 2005). It would have narrowed the statutory definition of "navigable waters" and defined certain isolated wetlands that are not adjacent to navigable waters, or non-navigable tributaries and other areas (such as waters connected to jurisdictional waters by ephemeral waters, ditches or pipelines), as not being subject to federal regulatory jurisdiction. Legislation similar to the Clean Water Authority Restoration Act of 2005 was introduced in the 110 th Congress ( H.R. 2421 and S. 1870 , a slightly different bill). The House Transportation and Infrastructure Committee held hearings on H.R. 2421 and related jurisdictional issues in July 2007, and a third hearing in April 2008. The Senate Environment and Public Works Committee held a non-legislative hearing on issues related to the Rapanos and SWANCC rulings in December 2007, and a legislative hearing on S. 1870 in April 2008. Proponents of legislation contend that Congress must clarify the important issues left unsettled by the Supreme Court's 2001 and 2006 rulings and by the Corps/EPA guidance. Bill sponsors argued that the legislation would "reaffirm" what Congress intended when the CWA was enacted in 1972 and what EPA and the Corps had subsequently been practicing until recently, in terms of CWA jurisdiction. However, critics asserted that by making activities that affect waters of the United States (in addition to discharges) subject to the CWA's jurisdiction, the legislation would expand federal authority, and thus would have consequences that are likely to increase confusion, rather than settle it. Critics questioned the constitutionality of the bill, arguing that, by including all non-navigable waters in the jurisdiction of the CWA, it would exceed the limits of Congress's authority under the Commerce Clause. Supporters contended that the legislation is properly grounded in Congress's commerce power. The Bush Administration did not take a position on any legislation to clarify the scope of "waters of the United States" protected under the CWA. Congressional attention resumed in the 111 th Congress, especially after statements by Obama Administration officials supporting the need for legislative clarification of these issues. In May 2009, the heads of EPA, the Corps, the Department of Agriculture, the Department of the Interior, and the Council on Environmental Quality jointly wrote to congressional leaders to identify certain principles that might help guide legislative and other actions: Broadly protect the nation's waters; make the definition of covered waters predictable and manageable; promote consistency between CWA and agricultural wetlands programs; and recognize long-standing practices, such as exemptions now in effect only through regulations or guidance. A modified version of legislation from the previous Congress was introduced in the Senate ( S. 787 , the Clean Water Restoration Act), and in June 2009, the Senate Environment and Public Works approved it with an amendment in the nature of a full substitute to the bill as introduced. As approved by the committee, S. 787 would have deleted "navigable waters" from the CWA and use "waters of the United States" directly to define jurisdiction. It defined "waters of the United States" by a rewritten version of the regulatory definition in use by EPA and the Corps: The term "waters of the United States" means all waters subject to the ebb and flow of the tide, the territorial seas, and all interstate and intrastate waters including lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, and natural ponds, all tributaries of any of the above waters, and all impoundments of the foregoing. In response to prior criticism, the definition did not encompass activities that affect waters of the United States (see above). The bill as reported also instructed that "waters of the United States" be construed consistently with (1) how EPA and the Corps interpreted and applied "waters of the United States prior to January 9, 2001, the day before SWANCC was decided, and (2) Congress's constitutional authority. The bill would have excluded, as in current EPA-Corps regulations, prior converted cropland and waste treatment systems. It also included a savings section that referenced without paraphrasing eight provisions in CWA Sections 402(l) and 404(f) which exempt certain types of discharges from CWA permits, such as discharges from normal farming activities, and discharges from maintenance of drainage ditches. The full Senate did not take up the bill. Legislation similar to the bills in the 111 th Congress has not been re-introduced, while bills were introduced to block EPA and the Corps from issuing revised "waters of the United States" guidance. In the 114 th Congress, bills to narrow the statutory definition of waters that are subject to CWA jurisdiction have been introduced, as has legislation to bar EPA and the Corps from issuing a revised "waters of the United States" rule or to require the agencies to re-start the rulemaking process for such a regulation. The Senate and House passed a resolution of disapproval under the Congressional Review Act ( S.J.Res. 22 ), which the President vetoed. The Senate was unable to override the veto. (For details, see CRS Report R43943, EPA and the Army Corps' "Waters of the United States" Rule: Congressional Response and Options , by [author name scrubbed].) In light of the widely differing views of proponents and opponents, future prospects for legislation on the geographic scope of CWA jurisdiction are highly uncertain. One difficulty of legislating changes to the CWA in order to specify which waters and wetlands are subject to the act's jurisdiction results from the fact that the complex scientific questions about such areas are not easily amenable to precise resolution in law. Debates over whether and how to revise the act highlight the challenges when debates over science, law, and policy intersect.

Summary: In 1985 and 2001, the Supreme Court grappled with issues as to the geographic scope of the wetlands permitting program in the federal Clean Water Act (CWA). In 2006, the Supreme Court rendered a third decision, Rapanos v. United States, on appeal from two Sixth Circuit rulings. The Sixth Circuit rulings offered the Court a chance to clarify the reach of CWA jurisdiction over wetlands adjacent only to nonnavigable tributaries of traditional navigable waters—including tributaries such as drainage ditches and canals that may flow intermittently. (Jurisdiction over wetlands adjacent to traditional navigable waters was established in the 1985 decision.) The legal and policy questions associated with Rapanos—regarding the outer geographic limit of CWA jurisdiction and the consequences of restricting that scope—have challenged regulators, landowners and developers, and policymakers for 40 years. The answer may determine the reach of CWA regulatory authority for all CWA programs, since the CWA uses but one jurisdiction-defining phrase ("navigable waters") throughout the statute. The Court's decision provided little clarification, however, splitting 4-1-4. The four-Justice plurality decision, by Justice Scalia, said that the CWA covers only wetlands connected to relatively permanent bodies of water (streams, rivers, lakes) by a continuous surface connection. Justice Kennedy, writing alone, demanded a substantial nexus between the wetland and a traditional navigable water, using an ambiguous ecological test. Justice Stevens, for the four dissenters, would have upheld the existing broad reach of Corps of Engineers/EPA regulations. Because no rationale commanded the support of a majority of the Justices, lower courts are extracting different rules of decision from Rapanos for resolving future cases. Corps/EPA guidance issued in 2008 says that a wetland generally is jurisdictional if it satisfies either the plurality or Kennedy tests. In 2011, the agencies proposed revised guidance intended to clarify whether waters are protected by the CWA, but this proposal was controversial and was not finalized. The ambiguity of the Rapanos decision and questions about the agencies' guidance increased pressure on EPA and the Corps to initiate a rulemaking to promulgate new regulations, which they did with regulatory revisions to define "waters of the United States" that are subject to CWA jurisdiction, issued in May 2015. (For discussion of this rule, seeCRS Report R43455, EPA and the Army Corps' Rule to Define "Waters of the United States"). The rule has been very controversial, including among Members of Congress. (For discussion, see CRS Report R43943, EPA and the Army Corps' "Waters of the United States" Rule: Congressional Response and Options, by [author name scrubbed] ). Challenges to the rule, called the Clean Water Rule, have been brought in a number of federal courts, and the rule has been stayed for the duration of litigation. While regulators and the regulated community debate the legal dimensions of federal jurisdiction under the CWA, scientists contend that there are no discrete, scientifically supportable boundaries or criteria along the continuum of wetlands to separate them into meaningful ecological or hydrological compartments. Wetland scientists believe that all such waters are critical for protecting the integrity of waters, habitat, and wildlife downstream. Changes in the limits of federal jurisdiction highlight the role of states in protecting waters not addressed by federal law. From the states' perspective, federal programs provide a baseline for consistent, minimum standards to regulate wetlands and other waters. Most states are either reluctant or unable to take independent steps to protect non-jurisdictional waters through legislative or administrative action.