The quality of the US most polluted waters has improved enormously over the past 20 years, largely as a result of strong action taken to control pollution from sources such as muncipal wastewater treatment plants and industrial discharges. Ironically, however, some of the cleanest waters have continued to degrade because pollution from other more diffuse sources, such as urban and agricultural run-off, is harder to control. Although effective in protecting drinking water, the current patchwork of federal, state, and local regulations does not consider the full range of benefits provided by watersheds in an intergrated way, according to a new report from a committee of the National Research Council.