National Aquatic Resource Surveys

National Rivers and Streams Assessment 2008-2009 Results

The NRSA 2008-2009 report presents the results of an unprecedented national scale sampling effort undertaken by the U.S. EPA and its state and tribal partners.

Reports and Data

National Rivers and Streams Assessment 2008-2009 Results Slideshow

The National Rivers and Streams Assessment (NRSA) 2008-2009 report provides information on the biological and recreational condition of the nation’s rivers and streams and the key stressors that affect them. It also reports out on changes in stream condition compared to an earlier study, the 2004 Wadeable Streams Assessment.
Background: During the summers of 2008 and 2009, 85 field crews sampled 1,924 river and stream sites across the country, representing nearly 1.2 million miles. Using standardized field methods, they sampled waters as large as the Mississippi River and as small as mountain headwater streams. Sites were selected using a random sampling technique based on a probability-based design. This design ensures that the results reflect the full variety of rivers and streams across the U.S.
Biological condition is the most comprehensive indicator of water body health. When the biology of a stream is healthy, the chemical and physical components of the stream are typically in good condition.
The primary biological indicator used in the NRSA 2008/09 is based on macroinvertebrates (aquatic insects and other creatures such as snails and crayfish). Macroinvertebrates respond to pollution in predictable ways.
Findings for Biological Condition: The NRSA 2008/09 finds that 28% of the nation’s river and stream length is in good biological condition for macroinvertebrates, 25% is in fair condition, and 46% is in poor condition.
Chemical Stressors: Four chemical stressors were assessed in the NRSA 2008/09: total phosphorus, total nitrogen, salinity, and acidification. These stressors were selected because of concerns about the extent to which they might be affecting the quality of biological communities in rivers and streams.
Findings for Nutrients: Phosphorus and nitrogen are the most widespread stressors to rivers and streams. NRSA 2008-09 found that 46% of the nation’s river and stream length has high levels of phosphorus.
Findings for Nutrients continued: The NRSA found that 41% of the nation's river and stream length has high levels of nitrogen. Excess nutrients can harm biological integrity. Poor biological condition (for macroinvertebrates) is almost twice as likely in rivers/streams with high levels of phosphorus and nitrogen.
Physical Habitat: Four indicators of physical habitat condition were assessed for the NRSA 2008/09: 1) excess streambed sediments, 2) riparian vegetative cover (vegetation in the land corridor surrounding the river or stream), 3) riparian disturbance (human activities near the river or stream, such as construction, agriculture, or vegetation removal), and 4) in-stream fish habitat (boulders, vegetation, logs and other types of valuable fish habitat and cover).
Findings for Physical Habitat Condition: The most widespread problems are poor riparian vegetative cover and high levels of riparian disturbance, reported in 24% and 20% of the nation’s river and stream length, respectively. However, the greater impact on biological condition results from excess levels of streambed sediments, reported in 15% of river and stream length. Poor biological condition is about twice as likely in rivers and streams with excessive levels of streambed sediments.
Human Health: The NRSA 2008/09 also assessed mercury in fish tissue and bacteria to provide insight into potential risks to human health. Human health screening values for mercury in fish tissue are exceeded in 13,144 miles of U.S. rivers (streams were not evaluated). In 23% of river and stream length, bacteria samples exceed an enterococci threshold level for protecting human health.
Changes in Stream Condition: Compared to the findings of the 2004 Wadeable Streams Assessment, some statistically significant changes are found in stream condition. Biological quality (based on macroinvertebrates) declined by 9% and phosphorus conditions declined by 14%. Indicators measuring riparian vegetation cover and riparian disturbance improved by 10% and 12% respectively.
Summary and Implications:The NRSA 2008/09 finds that many water quality problems remain to be addressed. Almost half of U.S. rivers and streams are in poor biological condition. Phosphorus, nitrogen, and streambed sediments in particular have widespread and severe impacts; reducing their levels will significantly improve the biological health of rivers and streams.
This survey suggests the need to address the many sources of these stressors — including runoff from urban areas, agricultural practices, and wastewater — in order to ensure healthier waters for future generations.