Each state map includes a bar chart of the combined number of miles of streams, rivers, and coastal shoreline or acres of lakes, estuaries and wetlands that do not meet state standards, and the pollutant that is causing the impairment. The pollutants most frequently identified as causing water pollution include sediments, excess nutrients, and harmful pathogens. Toxics, including metals, mercury and pesticides, also contribute to these impairments.
A TMDL is a pollution budget for a specific river, lake or stream. It is a quantitative estimate of what it takes to achieve state water quality goals in polluted waters. States review water quality conditions and identify specific waters that are polluted and work with local governments and interested parties in a cooperative, bottom-up process to develop TMDLs. In the TMDL process, states and local interests work together to allocate pollution reduction responsibility among sources and determine the most common sense, cost-effective way to address the specific problems of a particular waterbody.
EPA has proposed to strengthen the TMDL program, first authorized in the 1972 Clean Water Act, to clean up waters in communities across the country.