The federal Clean Water Act requires that states and tribes restore and maintain the chemical, physical, and biological integrity of the nation's waters. States and tribes must adopt water quality standards necessary to protect fish, shellfish, and wildlife while providing for recreation in and on the waters whenever possible.

Section 303(d) of the Clean Water Act establishes requirements for states and tribes to identify and prioritize water bodies that are water quality limited (i.e., water bodies that do not meet water quality standards). States and tribes must periodically publish a priority list of impaired waters, currently every two years. For waters identified on this list, states and tribes must develop water quality improvement plans known as total maximum daily loads (TMDLs) that establish allowable pollutant loads set at levels to achieve water quality standards.

The lower Boise River is a 64-mile stretch of river that flows through Ada County, Canyon County, and the city of Boise, Idaho. The river flows in a northwesterly direction from its origin at Lucky Peak Dam to its confluence with the Snake River near Parma, Idaho. Major tributaries include Fifteenmile Creek, Mill Slough, Mason Creek, Indian Creek, Conway Gulch, and Dixie Drain. View the subbasin assessment for these tributaries here.

Of the seven listed pollutants, only sediment and bacteria require TMDLs. Pollutant targets are based on existing water quality criteria for bacteria and on a numeric interpretation of the state narrative standard for sediment. Because the lower Boise River is a major tributary to the lower Snake River, phosphorus (total and dissolved) will be examined for possible load and waste load allocations after completion and approval of the Snake River-Hells Canyon TMDL.

Load allocations for temperature are not recommended for the lower Boise River segments listed for temperature since it has been found that atmospheric conditions preclude compliance with cold water biota temperature criteria during June, July, and August.

The U.S. Environmental Protection Agency does not believe that flow (or lack of flow) is a pollutant as defined by the Clean Water Act. Since TMDLs are not required for water bodies impaired by pollution but not pollutants, a TMDL was not developed for flow alteration.