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Columbia River

TMDL for Temperature in the Columbia and Lower Snake Rivers

What is a TMDL?

A TMDL is a calculation that identifies the amount of a pollutant (in this case, heat) that a river or other waterbody can receive and still meet specific standards developed by a state or tribe to protect water quality.

If the waterbody does not meet these standards for certain pollutants, it is considered impaired for those pollutants and a TMDL must be developed.

The EPA assists states, territories, and authorized tribes in submitting lists of impaired waters and developing TMDLs. Learn more about TMDLs.

On May 18, 2020, EPA issued for public review and comment the Total Maximum Daily Load (TMDL) for temperature on the Columbia and Lower Snake Rivers (see "Documents" below).

The TMDL addresses portions of the Columbia and lower Snake Rivers that have been identified by the states of Washington and Oregon as impaired due to temperatures that exceed those states' water quality standards.

See "Documents" below to view all comments received by EPA during the public comment period from May 21 through August 20, 2020 (extended from July 21).

After considering comments, EPA may make modifications, as appropriate, and then transmit the TMDL to Oregon and Washington for incorporation into their current water quality management plans.

Questions? Contact Mary Lou Soscia (, 503-326-5873, or Jill Nogi (, 206-553-1841.


You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.