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National Aquatic Resource Surveys

National Rivers and Streams Assessment

The National Rivers and Streams Assessment (NRSA) is a collaborative survey that provides information on the ecological condition of the nation’s rivers and streams and the key stressors that affect them, both on a national and an ecoregional scale. 

  • Time-lapsed photo of a stream 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. 
  • Map of the contiguous United States showing all the sites sampled during the NRSA 2008-2009 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.
  • Photo of a trainer demonstrating macroinvertebrate sampling in a wadeable stream 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. 
  • Graph showing the percentage of nation's river and stream length in good, fair, and poor biological condition for macroinvertebrates 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.
  • Collecting water samples in a wadeable stream 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.
  • Graph showing the percentage of nation's river and stream length in good, fair, and poor condition for total phosphorus 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.
  • Graph showing the percentage of the nation's river and stream length in good, fair, and poor condition for total nitrogen 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.
  • Sampling team assessing physical habitat in an urbanized stream 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).
  • Field crew taking measurements across a stream channel as part of the National Rivers and Streams Assessment 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.
  • Field crew recording data during the National Rivers and Streams Assessment 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.
  • Graph showing the change in the percent of stream length in good condition of various indicators between WSA 2004 and NRSA 2009 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.
  • Time-lapsed photo of a stream 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.