The U.S. Environmental Protection Agency (EPA) is in the process of redesigning the Clean Water Act's (CWA's) total maximum daily load (TMDL) program. Section 303 of the Act requires states and, if necessary, EPA to: (1) identify waters that do not meet water quality standards; (2) establish the TMDLs for pollutants discharged into these waters that will achieve these standards; and (3) incorporate these loads into state planning. These are of course the classic steps of ambient-based water quality management.

Ambient-based management has not worked well in any media—air, water, or waste. It requires enormous amounts of data. It requires analysis that is rarely definitive and nearly always litigable. It launches a process that never ends. These same factors plagued the CWA's predecessors and the similarly constructed Clean Air Act (CAA). They have prolonged and frustrated decisions under federal pesticide, toxic substances, safe drinking water, hazardous waste, and Superfund laws as well. EPA's task with TMDLs is not an easy one, then, under the best of circumstances.