This 2000 National Water Quality Inventory report is the 13th in a series published since 1975 under Section 305(b) of the Clean Water Act. Section 305(b) requires states to describe the quality of their waters; the U.S. Environmental Protection Agency (EPA) must then summarize these assessments and transmit that summary report to Congress. Please note that, pursuant to Public Law 104-66 (the Federal Reports Elimination and Sunset Act of 1995), this edition of the Inventory is not considered a Report to Congress. In their 2000 reports, states, tribes and other jurisdictions assessed 19% of the nation’s stream miles; 43% of its lake, pond, and reservoir acres; and 36% of its estuarine square miles. The states also assessed the quality of their ocean coastline, Great Lakes shoreline, wetlands, and ground water. The information contained in this report applies only to the waters assessed. The states found that approximately 60% of assessed stream miles, 55% of assessed lake acres, and 50% of assessed estuarine square miles fully supported the water quality standards set for them, although significant proportions of these waters were threatened and might degrade in the future. The remaining assessed waters were impaired to some degree. Leading causes of impairment reported by the states in 2000 include bacteria, siltation, nutrients, and metals (primarily mercury). Sources of impairment include agricultural activities, hydrologic modifications (such as channelization, dredging, or flow regulation), municipal sources, and urban runoff/storm sewers. The percent of assessed stream and estuarine waters found to be impaired overall has increased somewhat from the last report in 1998, although that difference is more likely due to changes in monitoring approaches than actual water quality degradation. In 2000, metals (primarily mercury) were the leading cause of impairment in the nation’s estuaries (up from third leading cause in 1998); in lakes, metals were again the second leading cause of impairment. Increasingly, states are moving toward more comprehensive examination of fish tissue and are issuing statewide advisories that restrict the consumption of selected fish species, especially for vulnerable segments of the population. Mercury, which originates from air transport from power generating facilities and incinerators, mining, natural rock weathering, and other sources, was cited in approximately 2,240 of the 2,800 fish consumption advisories reported in 2000. In the past, data collection and interpretation efforts under the Clean Water Act were not always coordinated. The EPA has been working with its partners to streamline and combine Section 305(b) water quality reporting requirements with those of Section 303(d) (which requires states to identify impaired waters and develop allocations of the maximum amount of a pollutant each impaired water can receive and still meet water quality standards). EPA has also developed guidance providing details on water monitoring designs, data quality and data quantity needs, and data interpretation methods under this combined approach. You can learn more about these monitoring initiatives by visiting our website at www.epa.gov/owow/monitoring.