United States Office of Water 

Environmental Protection 4304T October 2002 

Agency 

EPA-822-F-02-008 

FACT SHEET 

ECOREGIONAL NUTRIENT CRITERIA

Summary 

The U.S. Environmental Protection Agency (EPA) is finalizing nine nutrient water quality criteria 

documents, and publishing three new nutrient water quality criteria documents for lakes and 

reservoirs, and rivers and streams within specific geographic regions (ecoregions) of the United 

States. The nine nutrient water quality criteria documents were first announced in the February 28, 

2002 Federal Register. After addressing peer review and review of significant scientific information 

provided by the public, EPA has finalized the nine criteria documents. 

EPA’s recommended section 304(a) water quality criteria for nutrients were developed with 

the aim of reducing and preventing eutrophication on a national scale. Each document presents 

recommended criteria for causal parameters (total phosphorus and total nitrogen) and response 

variables (chlorophyll a and some form of water clarity, i.e., turbidity or Secchi depth). This 

information is intended as a starting point for states, authorized tribes and others to develop more 

refined nutrient criteria, as appropriate, using EPA waterbody–specific technical guidance manuals 

and other scientifically defensible approaches. EPA will work with states and authorized tribes as 

they adopt water quality criteria for nutrients into their water quality standards. 

Background

EPA issued seventeen ecoregional 

nutrient criteria documents in January 

2000. EPA’s nutrient website 

(www.epa.gov/ost/standards/nutrient.html) 

presents the geographic coverage 

and the recommended nutrient water 

quality criteria for each nutrient ecoregion 

(There are a total of fourteen nutrient 

ecoregions). With the two actions 

announced today, EPA has published 

nutrient criteria recommendations for 26 

nutrient ecoregions, and is requesting 

significant scientific information from the 

public on three additional ecoregions. 

Why is EPA publishing Ecoregional 

Nutrient Criteria? 

The national goals of the Clean Water Act 

are to achieve, wherever attainable, water 

quality which provides for the protection 

and propagation of fish, shellfish, and 

wildlife and recreation in and on the water. 

As part of state and tribal water quality 

standards, the Clean Water Act requires 

states and authorized tribes to specify 

designated uses for their waters in 

consideration of these goals, and to adopt 

water quality criteria that protect those 

designated uses. To help states and tribes, 

EPA develops and publishes national criteria 

guidance and information. This information 

presents the latest scientific knowledge on the 

effects of pollutants on biological community 

diversity, productivity, and stability, including 

information on the factors affecting rates of 

eutrophication (excess amounts of nutrients 

that stimulate undesirable plant growth) for 

receiving waters. 

Overview of the Problem 

Eutrophication of United States surface waters 

is a long standing problem. As much as half of 

the Nation’s waters surveyed by states and 

tribes do not adequately support aquatic life 

because of excess nutrients. Nitrogen and 

phosphorus are the primary causes of 

eutrophication and resulting algal blooms. 

Chronic symptoms of overenrichment include 

low dissolved oxygen, fish kills, cloudy murky 

water, and depletion of desirable flora and 

fauna. Nutrient levels that lead to these 

problems vary from one region of the country to 

another due to geographical variations in 
geology, climate and soil types. In order to 

be most effective, therefore, state and tribal 

water quality criteria need to take into 

account ecoregional variations. 

What are ecoregional nutrient criteria 

and how should they be used? 

Nutrient criteria are numerical values for 

both causative (phosphorus and nitrogen) 

and response (chlorophyll a and turbidity) 

variables associated with the prevention 

and assessment of eutrophic conditions. 

EPA’s recommended ecoregional nutrient 

criteria represent conditions of surface 

waters that have minimal impacts caused 

by human activities. Therefore, when a 

state or tribe applies these criteria, the 

waters are protected from the harmful 

consequences of nutrient overenrichment. 

These recommended water quality criteria 

are suggested baselines which states and 

tribes should refine to help identify problem 

areas, serve as a basis for state and tribal 

water quality criteria for nutrients, and 

evaluate relative success in reducing 

eutrophication. 

What are the activities

related to these criteria documents?

EPA published a Notice of Availability in the 

Federal Register to solicit scientific views 

on the criteria documents. EPA will review 

and consider new information submitted by 

the public on significant scientific issues 

and site-specific data. EPA will also forward 

pertinent data submitted by the public to 

the appropriate Region to help develop 

more refined local criteria. 

The criteria have been through external 

peer review, and a summary of these 

comments are available on the Nutrient 

website 

(www.epa.gov/ost/standards/nutrient.html) 

Publication of these three nutrient criteria 

documents completes EPA’s nutrient 

criteria development for freshwater 

waterbodies of the United States. EPA 

intends to develop ecoregional nutrient 

criteria for wetlands as well as specific 

estuarine and coastal waters in the near 

future. 

What are EPA’s expectations for these 

criteria? 

EPA expects that states and tribes will use 

these three ecoregional nutrient criteria 

documents as starting points to identify more 

precise numeric levels for nutrient parameters 

needed to protect aquatic life, recreational, or 

other uses on site-specific or subregion-specific 

conditions. EPA expects these more precise 

numerical levels to be developed on a smaller 

geographic scale than the ecoregional values 

presented in the nutrient water quality criteria 

documents. States and tribes may also 

develop criteria using other scientifically 

defensible methods and appropriate water 

quality data or simply adopt EPA’s 

recommended water quality criteria in their 

water quality standards. EPA expects states 

and tribes to prepare a plan for adopting 

nutrient criteria and to adopt new or revised 

nutrient criteria into their water quality 

standards. 

Will these criteria be revised in the future? 

After we review the submitted significant 

scientific information, EPA may publish either 

revised criteria or a notice informing the public 

that it does not intend to revise the documents 

presently. EPA will, however, update the 

criteria as new scientific information becomes 

available. 

How do I obtain a copy of the documents? 

You can get copies of the complete set of three 

ecoregional criteria documents, or a specific 

ecoregional criteria document from EPA’s 

National Service Center for Environmental 

Publications (NSCEP), 11029 Kenwood Road, 

Cincinnati, OH 45242; (513) 489-8190 or toll 

free (800) 490-9198. You can also get copies 

by contacting the Water Resource Center at 

(202) 260-7786. Alternatively, consult EPA’s 

nutrient website at 

www.epa.gov/ost/standards/nutrient.html for 

downloads. EPA’s waterbody-specific technical 

guidance manuals, which present the Agency’s 

recommended nutrient criteria derivation 

methodology, are also available at this website.