In 2005, the U.S. Environmental Protection Agency (EPA) began a new program to assess the condition of the nation’s water resources. Partnering with the states, tribes and other agencies, EPA launched the National Aquatic Resource Surveys (NARS). The goals of the surveys are to quantify the health of the nation’s waters based on a set of physiochemical and biological indicators, and to identify the relative importance of key stressors, including nitrogen and phosphorus. Each survey uses standardized field and lab methods and is designed to produce unbiased estimates of the condition of the whole water resource being studied (i.e., rivers and streams, lakes and reservoirs, wetlands, or coastal waters). 

• Nitrogen and Phosphorus Pollution in the Mississippi River Basin: Findings of the Wadeable Streams Assessment (PDF)(2 pp, 2 MB, December 2011, EPA 841-F-11-004)