Abstract

This entry defines “total maximum daily load” (TMDL) and describes its role in the Federal Water Pollution Control Act, more commonly known as the Clean Water Act. A TMDL is one of the Act's mechanisms for ensuring that all water bodies in the United States eventually meet the water quality standards that states or the Environmental Protection Agency set for them. Water quality standards, in turn, define the ultimate water quality goals for individual water bodies. More specifically, a TMDL is the mechanism through which states and the Environmental Protection Agency (EPA) modify discharge permits; it can also prompt states to improve state nonpoint source management requirements (such as best management practices) to ensure that all water bodies actually achieve their water quality standards. This entry also describes several of the legal and pragmatic issues that have arisen in the TMDL regime.