TMDL Title: Snake River- Hells Canyon TMDL and WQMP
Water Quality Limited Parameters: total mercury, methylmercury
Pollutants: total mercury, methylmercury
Status: In development
Project Summary
The Snake River is the largest tributary of the Columbia River. The Snake River headwaters originates in the Greater Yellowstone Area, Wyoming and flows west across southern Idaho until meeting the Oregon-Idaho border and turning north until it meets the Columbia River. The scope of this TMDL will focus on a portion of the Snake River from where it meets the Oregon Border to the Washington-Oregon-Idaho Border. There are three privately owned hydroelectric dams in the project area; Brownlee Dam, Oxbow Dam, and Hells Cayon Dam, which collectively are known as the Hells Canyon Complex.
Assessment units in the Snake River-Hells Canyon do not meet water quality standards for methylmercury. DEQ establishes water quality standards to protect the health of waterways for beneficial uses, such as recreational activities or fish and wildlife habitat. Oregon is required to establish a Total Maximum Daily Load (TMDL) for waters that do not meet water quality standards. The TMDL for each pollutant is determined through an analysis to calculate the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards.
DEQ is currently developing a mercury and methylmercury TMDL for the Snake River-Hells Canyon to protect for the human consumption of fish. Other TMDLs under development in the Snake River include a temperature TMDL replacement project. Information on the existing Snake River TMDL can be found below.
For requesting data, models or other information used in this TMDL, please complete a "Public Records Request".
For more information and to review important studies on mercury and methylmercury in the Hells Canyon Complex please visit the USGS Mercury Cycling Hells Canyon Complex website.
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