An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

National Aquatic Resource Surveys

History of the National Aquatic Resource Surveys

Under the Clean Water Act (CWA), the U.S. Environmental Protection Agency must periodically report on the condition of the nation's water resources by summarizing water quality information provided by the states. However, approaches to collecting and evaluating data vary from state to state, making it difficult to compare the information across states, on a nationwide basis, or over time.

In the early 2000s, a number of independent organizations, including the Government Accountability Office and the National Research Council, noted that EPA and the states did not have a uniform, consistent approach to answer key questions about water quality. In response, EPA, states, tribes, academics and other federal agencies began collaborating on a series of statistically based surveys called the National Aquatic Resource Surveys (NARS) to provide the public and decision-makers with improved, statistically-valid environmental information.

The Wadeable Streams Assessment (WSA), published in 2006, was the first report in this series, and the first nationally-consistent, statistically-valid study of the nation’s wadeable streams. It was followed by the first National Lakes Assessment (NLA 2007). Additional reports in this series are being prepared in a rotating basis, by waterbody type. 

NARS is based on the work of the EPA’s Environmental Monitoring and Assessment Program (EMAP). EMAP was a research program run by EPA’s Office of Research and Development (ORD) to develop the tools necessary to monitor and assess the status and trends of national ecological resources. EMAP collected field data from 1990 to 2006. Its goal was to develop the scientific understanding for translating environmental monitoring data from multiple spatial and temporal scales into assessments of current ecological condition and forecasts of future risks to our natural resources.

EMAP aimed to advance the science of ecological monitoring and ecological risk assessment, guide national monitoring with improved scientific understanding of ecosystem integrity and dynamics and demonstrate multi-agency monitoring through large regional projects. EMAP developed indicators to monitor the condition of ecological resources. It also investigated designs that addressed the acquisition, aggregation and analysis of multi-scale and multi-tier data.

EMAP publications and results are found on the EMAP website.