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.

This document is a subbasin assessment only. It describes the physical, biological, and cultural setting; water quality status; pollutant sources; and recent pollution control actions in the upper Boise River watersheds.

Located in southwest Idaho, the upper Boise River Subbasin is about 2,033 square miles of predominantly undeveloped forest land and open range with both managed and free flowing streams. The upper Boise River Subbasin is comprised of the two hydrologic cataloging units of the Boise River system upstream of Arrowrock Reservoir. The waters of the subbasin join to form the Arrowrock Reservoir, which supplies water to Lucky Peak Reservoir and the lower Boise River.

This subbasin assessment has documented that all §303(d) listed water bodies within the upper Boise River Subbasin are currently fully supporting all of their beneficial uses and are no longer candidates for TMDL development.

The subbasin assessment also lists water bodies not fully supporting their beneficial uses that should be added to the §303(d) list during the next listing cycle.