In the 30 years since the passage of the Clean Water Act, Congress, the American Public and other interested parties have been asking the U.S. Environmental Protection Agency to describe the condition of the waters in the U.S. They want to know if there is a problem, how big the problem is if there is one, and whether the problem is widespread or occurs in hotspots. Additionally, they have been asking to understand the types of human activities that are affecting streams and rivers, and which are likely to be the most important. These are seemingly simple questions, and yet they have not been answered in a reliable way in the past. This report presents the results of a unique collaboration between the U.S. Environmental Protection Agency and twelve western States, designed to answer these questions for the rivers and streams of the West. The purpose of the assessment is fourfold: Report on the ecological condition of all perennial flowing streams and rivers with the exception of those considered Great Rivers, (the lower Columbia, Snake, Missouri and Colorado Rivers). Describe the ecological condition of western streams and rivers with direct measures of plants, fish, and other aquatic life. Identify and rank the relative importance of chemical, physical and biological disturbances affecting stream and river condition. Encourage states to include these design and measurement tools as a portion of their State monitoring programs, so that future condition assessments will be ecologically and statistically comparable both regionally and nationally.

"September 2005." "EPA/620/R-05/005." Includes bibliographical references (p. 29-31).

This report presents an ecological assessment of non-tidal streams and rivers across twelve states of the western U.S., based on the results of a unique and experimental monitoring program implemented through the U.S. EPA's Environmental Monitoring and Assessment Program (EMAP) during the years 2000-2004. The two major objectives were to document the overall condition of the vast network of streams and rivers of the western U.S. and to demonstrate the utility and flexibility of an EMAP-like approach to environmental monitoring and assessment at this regional scale. The assessment is divided into two major categories. The first is the measurement of the ecological condition of streams and rivers in the West by direct measurements of their resident biological assemblages: aquatic vertebrates and benthic macroinvertebrates. The second is an assessment of the relative importance of potential stressors on those assemblages, based on direct measures of their chemical, biological and physical habitat.