A recent regulatory program that will provide unique challenges and opportunities for the Corps of Engineers over the next 15 years or more is the Total Maximum Daily Load (TMDL) Program. According to the U.S. Environmental Protection Agency (USEPA 1999b), establishing a TMDL is part of a process whereby impaired or threatened water bodies and the pollutant(s) causing the impairment are systematically identified and a scientifically based strategy a TMDL-is established to correct the impairment or eliminate the threat and restore the water body. While the TMDL Program itself as administered by the EPA is relatively recent, the requirement for the program lies in the Clean Water Act (CWA) of 1972. The CWA contained a provision Section 303(d) requiring all states to develop and implement TMDLs for their impaired water bodies (those failing to meet water quality standards) and water bodies threatened to become impaired. This requirement has not been aggressively enforced until recently, largely because of the difficulties involved in that enforcement. While in the past regulatory control has focused on individual water bodies and point sources, under the TMDL process all sources (point and non-point) must be considered (USEPA 1991, 1999a, 1999b, 1999f), which poses unique scientific and regulatory challenges. The TMDL process is essentially driving the watershed approach to water quality management (YSI 1999).