Columbia & Snake River temperature TMDL

The Columbia and Lower Snake Rivers are listed on the state's polluted waters list for high water temperatures that are above Washington water quality standards and can harm salmon. Because the Columbia and Snake Rivers cross multiple state boundaries and span almost 900 miles, the federal Environmental Protection Agency (EPA) published the Total Maximum Daily Load (TMDL) for temperature in the Columbia and Lower Snake Rivers on May 20, 2020. EPA held a public comment period in summer of 2020 and reissued the final TMDL on Aug. 13, 2021. We are in early stages of planning implementation. 

Learn more from our blog post.

Columbia River view with houses along shore

EPA's TMDL covers almost 900 miles of the Columbia and Lower Snake Rivers.

Water temperature issues 

Temperature levels in the Columbia and Lower Snake Rivers are particularly high during summer months, from June through October. These rivers are important areas for salmon to live, spawn, and migrate. EPA's TMDL plan addresses portions of the Columbia and Lower Snake Rivers that span almost 900 miles. The Columbia River spans from the Canadian border to the Pacific Ocean and the Lower Snake spans from the Idaho border to where it connects with the Columbia River. Because of the large scope of this project, we are working with many partners to address temperature in these rivers.

Salmon need cool and clean water to survive. Water temperature influences the health of many organisms that live in a water body and cooler water holds more dissolved oxygen, which fish and other aquatic life need to breathe. We set our water quality temperature standards at the levels salmon need for spawning, migration, and livable habitat. Approximately 2-3 million adult salmon and steelhead return from the ocean to the Columbia River each year. We are dedicated to protecting salmon in these rivers.

Ecology works on many issues in the Columbia River. To learn about our other work in the Columbia River, visit the Office of the Columbia River webpage.  

Developing a water cleanup plan

Typically, Ecology is responsible for publishing TMDLs to address water quality issues in Washington. Because the Columbia and Lower Snake Rivers cross so many boundaries, EPA is responsible for publishing this TMDL. EPA's TMDL identifies temperature sources to the Columbia and Lower Snake Rivers and assigns a temperature allocation, or the maximum amount of a temperature a source can contribute to the river. The TMDL focuses on assigning allocations to dams, tributaries, and point sources. It is Ecology's responsibility to implement the TMDL in Washington so we can work towards meeting Washington's water quality standards.

We will draft an implementation plan that will describe our strategy for meeting temperature standards and how we will partner and work together with temperatures sources to address their impacts in the Columbia and Lower Snake Rivers. We are in the early stages of implementation planning, but our plan will include our strategy for working with dams, updating permits for point sources, and prioritizing tributary work to address high river temperatures and to protect salmon.

TMDL documents

Past stakeholder and tribal meeting materials

Jan. 28, 2021

If you're interested in receiving updates on Ecology's plan for implementation and upcoming stakeholder and tribal meetings, please email