The National Rivers and Streams Assessment 

2008-2009: A Collaborative Survey

www.epa.gov/aquaticsurveys

he National Rivers and Streams Assessment (NRSA) is a study of all rivers and streams of the U.S., from 

the largest “great rivers” to the smallest headwater streams. It was conducted using standard statistical 

survey techniques: sites were selected at random to represent the condition of all rivers and streams 

in regions that share similar characteristics. This is the first time a national monitoring study of the overall 

condition of streams and rivers has been conducted using this statistically-valid approach. State and tribal 

water quality agencies, with support from EPA, conducted this work using the same methods at all sites to 

ensure that results can be compared across the country.

Key Findings: Overall Biological Condition

•	 55% of the nation’s river and stream miles do not support 

healthy populations of aquatic life, with phosphorus and 

nitrogen pollution and poor habitat the most widespread 

problems. 

•	 23% of river and stream miles are in fair condition. 

•	 21% are in good condition and support healthy biological 

communities.

Leading Problems: Nutrient Pollution 

and Habitat Degradation 

•	 40% of the nation’s river and streams miles have high 

levels of phosphorus. 27% have high levels of nitrogen. 

•	 Biological communities are at increased risk for poor 

condition when phosphorus and nitrogen pollution levels 

are high. 

•	 Phosphorus and nitrogen pollution comes from excess 

fertilizers, wastewater and other sources, and can cause 

algae blooms, low oxygen levels, and more.

•	 Poor vegetative cover and high levels of human 

disturbance near river and stream banks are also 

widespread, reported in 24% and 20% of the nation’s river 

and stream miles respectively. 

•	 These habitat conditions make rivers and streams more 

vulnerable to flooding, contribute to erosion and allow 

more pollutants to enter waterways. 

•	 Excess levels of streambed sediments, which can smother 

the habitat where many aquatic organisms live or breed, 

are reported in 15% of river and stream miles. Excess 

sediments are found to have a significant impact on 

biological condition.

Poor

T

55% 

23% Poor

Fair

21% 

Good

Overall Biological Condition

Changes in Stream 

Condition

Compared to the 

findings of the 2004 

Wadeable Streams 

Assessment, the NRSA 

found some significant 

changes in stream 

condition: 

•	 7% fewer stream miles are in good 

biological condition;

•	 19% fewer stream miles are in good 

condition for phosphorus;

•	 9% more stream miles are in good 

condition for nitrogen; 

•	 17% more stream miles are in good 

condition for in-stream fish habitat; and

•	 12% more stream miles are in good 

condition as measured by riparian 

disturbance. 

These changes are for streams only, between 

two points in time; future surveys and 

additional data are needed to discern trends 

and the reasons for those trends. 
Human Health Indicators

Two indicators that provide insight into potential risks 

to human health were assessed: enterococci (bacteria) 

and mercury in fish tissue. The report finds that: 

•	 In 9% of U.S. river and stream miles, enterococci 

bacteria exceed thresholds protective of human 

health. 

•	 Over 13,000 miles of rivers are found to have 

mercury in fish tissue at levels that exceed 

thresholds protective of human health.

Implications of the Survey

Our rivers and streams are under significant 

stress. Reducing nutrient pollution and 

improving habitat will significantly improve 

the biological health of rivers and streams and 

support important uses such as swimming and 

fishing. This survey suggests that, although 

many actions are underway to protect our 

rivers and streams, we need to address the 

many sources of pollution — including runoff 

from urban areas, agricultural practices, and 

wastewater — in order to ensure healthier 

waters for future generations.

Small streams, such as headwater streams, 

are a critical part of the ecosystem and 

provide food and shelter to a broad array of 

aquatic organisms, birds, and wildlife.

Researchers measured chemical 

pollutants such as nutrients, 

salinity, and acidification, 

as well as physical habitat 

characteristics such as 

streambed sediments and 

streambank vegetative cover. 

They then examined the 

relationship between these 

indicators and biological health.

Biological Condition by Ecological Region

The NRSA includes analysis of biological condition in each of the nine ecological regions of the U.S.

This biological rating is based on 

an index that combines different 

measures of the condition of aquatic 

macroinvertebrates (aquatic insects 

like the stoneflies pictured above and 

other creatures such as crayfish). 

Aquatic insects serve as excellent 

indicators of overall water quality. 

EPA has produced reports using a similar approach for other waterbody types (The Wadeable Streams Assessment, 

The National Lakes Assessment, and The National Coastal Condition Report). A report on national wetland condition 

is underway. To learn more about these National Aquatic Resource Surveys, visit www.epa.gov/aquaticsurveys.

March 2013, EPA 841-F-13-004