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 Hells Canyon section of the Snake River serves as the Idaho/Oregon border. Therefore, the Snake River�Hells Canyon TMDL was developed jointly by Idaho DEQ and Oregon DEQ.

The scope of the this TMDL extends from where the Snake River intersects the Oregon/Idaho border near Adrian, Oregon, to immediately upstream of the inflow of the Salmon River. This includes the Hells Canyon Complex reservoirs: Brownlee, Oxbow, and Hells Canyon. The overall reach has been divided into five segments based on similar hydrology, pollutant delivery, and processing mechanisms; and operational, management, and implementation strategies. The five segments are:

•  Upstream Snake River (river mile 409 to 335, 74 miles total)

•  Brownlee Reservoir (river mile 335 to 285, 50 miles total)

•  Oxbow Reservoir (river mile 285 to 272.5, 12.5 miles total)

•  Hells Canyon Reservoir (river mile 272.5 to 247, 25.5 miles total)

•  Downstream Snake River (river mile 247 to 188, 59 miles total)

Within these segments, all designated beneficial uses and the following listed pollutants have been addressed by the TMDL: bacteria, nutrients, nuisance algae, dissolved oxygen, pesticides, pH, sediment, temperature, and total dissolved gas. The document recommends that the segment addressed by this TMDL be delisted for bacteria and pH. The mercury TMDL has been postponed to 2006 due to a lack of water column data.

Recognizing the complexity of the Snake River�Hells Canyon system, the TMDL adopts a phased approach to implementation that will identify interim milestones to determine the effectiveness of management measures or other action controls being implemented. It also includes a process for reviewing and revising management approaches.

The TMDL document includes two separate, state-specific implementation plans. Together, these documents represent the water quality management plan for the Snake River�Hells Canyon TMDL.