Sediment discharge to the Boise River from Mason Creek.

The mainstem Boise River and some of its tributaries are water quality limited, or impaired by pollutants, in certain reaches. By figuring out exactly where the problems are, we can figure out the most effective solutions.

The entire mainstem Boise River has too much sediment. From Star to the Snake River, bacteria levels are also too high in the mainstem Boise River. Within the river, temperatures are elevated, phosphorous concentrations are high, and pathogens have also been found. Fishing and swimming, beneficial uses in the Boise River, are limited primarily by sediment and bacteria. Uses in the downstream Snake River are limited primarily by phosphorous, sediment, and bacteria. So, sediment, bacteria, and phosphorous are the current focus for pollutant reduction.

Multiple tributaries within the watershed, other than the mainstem segments of the lower Boise River, are listed as water quality limited. Since the tributaries are sources of pollutants to the Boise River, sediment and bacteria limits are provided in the tributaries TMDL.

Water quality standards are intended to provide protection for designated beneficial uses, which are the benefits the river is expected to be able to provide, primarily for humans and aquatic life. TMDL targets are based on these water quality standards. Designated uses for the Lower Boise mainstem are summarized below (designated uses for the tributaries are under potential revision).

These designated uses are specified by Idaho State law. The Lower Boise Watershed Council is the the process of potentially revisiting the designated uses for the tributaries using a process call a "Use Attainability Analysis."

Designated Uses Defined

Cold water biota and salmonid spawning: Conditions met for cold-water fishes and aquatic life.

Primary contact recreation: Any activity with the intended purpose of direct water contact by the human body to the point of complete submergence, including but not limited to swimming, water skiing, and skin diving.

Secondary contact recreation: Any activity occurring on or near the water, such as boating, wading, and rowing.

Domestic water supply: Source for drinking water supplies and often includes waters for food processing (may require further treatment before use).

Special resource water: Outstanding high quality water body with outstanding recreational or aesthetic qualities.

Agricultural water supply: Includes uses of water for stock watering, irrigation, and other farm purposes.