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Temperature TMDL Replacement: Willamette Subbasins

TMDL title: TMDLs for the Willamette Subbasins 
Water Quality Limited Parameters: Temperature
Pollutants: Heat

Status: Approved. The Willamette Subbasins TMDL for temperature was adopted by the Environmental Quality Commission into rule on Aug. 6, 2024. EPA approved the TMDL on Sept. 12, 2024. On May 8, 2025, the EQC adopted a rule amendment to include Willamette mainstem and major tributaries project area. The rule amendment is pending EPA action by June 28, 2025, to approve or disapprove the TMDL. 

Project Area: This TMDL project includes the following Willamette Subbasins: Coast Fork Willamette, McKenzie, Middle Fork Willamette, Upper Willamette, Middle Willamette, Molalla-Pudding, North Santiam, South Santiam, Lower Willamette, and Clackamas Subbasins.

This project does not include waterbodies in the Tualatin Subbasin and Yamhill Subbasin. 

Project summary

In 2013, the United States Environmental Protection Agency disapproved the Natural Conditions Criterion contained in Oregon's water quality standard for temperature due to the 2012 U.S. District Court decision for NWEA v. EPA, 855 F. Supp. 2d 1199 (D. Or., 2012). This portion of the temperature water quality standard was used in most temperature TMDLs issued from 2003 through 2012. On Oct. 4, 2019, the U.S. District Court issued a judgment for NWEA v. EPA, No. 3:12-cv-01751-HZ (D. Or., Oct. 4, 2019) and required DEQ and USEPA to replace 15 Oregon temperature TMDLs that were based on the Natural Conditions Criterion and to reissue the temperature TMDLs based on the remaining elements of the temperature water quality standard.

The temperature TMDLs for the Willamette Subbasins were developed in two phases. The first phase addressed temperature listings for waters upstream of the U.S. Army Corps of Engineers dams, PGE's River Mill dam on the Clackamas River, and the McKenzie-Willamette River confluence. The second phase included the mainstem Willamette River and all the major tributaries downstream of the dams. The exact extents are described in the Quality Assurance Project Plans listed below. The TMDLs were phased to consider the extent of the water quality models being used to support the TMDLs, schedule requirements of the court order, and DEQ's available resources.



The Quality Assurance Project Plans listed below summarize the modeling and analysis methods used for the replacement temperature TMDLs in the Willamette Subbasins project area. 

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Rulemaking 

TMDL development and implementation is a public process. DEQ developed this TMDL by rule per Oregon Administrative Rule Chapter 340 Division 42. During a rulemaking process, DEQ seeks public involvement by holding public hearings, establishing rule advisory committee meetings for technical and policy input, and for feedback regarding potential fiscal impacts related to the rule.

Willamette Subbasins TMDL and the amendment rulemakings

Advisory Committee Documents​​

Meeting 3: July 30, 2024

Meeting 2: May 16, 2024

Meeting 1: March. 14, 2024

Public Involvement

Supporting documents

Staff report: Willamette River Mainstem and Major Tributaries TMDL 



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Advisory committee documents

Meeting 2: April 6, 2023

Meeting 1:  Feb. 23, 2023

Sup​porting documents

Public Involvement Documents
EQC documents

Contact

Steve Mrazik, TMDL Water Quality Manager
Water Quality Management Plan, Basin Coordinators