The Clean Water Act (CWA) requires states to identify waters that are impaired by pollution, even after application of pollution controls. For these waters, states must establish a total maximum daily load (TMDL) of pollutants to ensure that water quality standards can be attained. Implementation was dormant until states and the Environmental Protection Agency (EPA) were prodded by numerous lawsuits. The TMDL program has become controversial, in part because of requirements and costs now facing states to implement this 30-year old provision of the law. In 1999, EPA proposed regulatory changes...