DEQ TMDL & 5-Year Review Overview

Section 303(d) of the Clean Water Act requires states and tribes to identify and prioritize water bodies that do not meet water quality standards through Idaho’s Integrated Report. Idaho must develop a water quality improvement plan, called a total maximum daily load (TMDL), for those water bodies not meeting water quality standards. A subbasin assessment is the first step toward developing a TMDL. Total Maximum Daily Loads (TMDLs) are water quality improvement plans that establish a pollutant budget for streams, rivers, or lakes with impaired water quality. Impaired water quality means the water does not meet Idaho’s Water Quality Standards for the protection of aquatic life, human health, or other beneficial uses. For most waters in Idaho, TMDLs are developed by the Idaho Department of Environmental Quality (DEQ) in conjunction with a Watershed Advisory Group ( WAG ). According to the Clean Water Act, the U.S. Environmental Protection Agency (EPA) ultimately approves the TMDLs.