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Temperature TMDL Replacement: Willamette Subbasins

TMDL title: Temperature TMDLs for the Willamette Subbasin (excludes Tualatin and Yamhill Subbasins).
Water Quality Limited Parameters: Temperature
Pollutants: Heat

Schedule: DEQ will present the Willamette Subbasins TMDL to the Environmental Quality Commission for proposed rule adoption in November 2023 to give EPA a minimum of 60 days for their approval or disapproval by Sept. 15, 2024.

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, Yamhill Subbasin, the Willamette River mainstem, and most of the major tributaries to the Willamette River. The temperature TMDLs for the Willamette River mainstem and major tributaries (exact extent summarized below) will be developed as a separate project with rule advisory meetings expected to begin in 2023 and scheduled for EPA approval or disapproval by Feb. 28, 2025.

Waterbodies in the Willamette mainstem and major tributaries project area include:

  • Willamette River including all side channels and sloughs from the confluence of the Columbia River to the confluence of Coast Fork of the Willamette and Middle Fork of the Willamette Rivers (approximately river mile 187);
  • Multnomah Channel:
  • Clackamas River up to River Mill Dam/Estacada Lake (approximately river mile 26);
  • Santiam River (all 12 miles)
  • North Santiam River up to Detroit Dam (approximately river mile 49)
  • South Santiam River up to Foster Dam (approximately river mile 38)
  • Long Tom River to Fern Ridge Dam (approximately river mile 26)
  • Middle Fork Willamette to Dexter Dam (approximately river 17)
  • Fall Creek to Fall Creek Dam (approximately river mile 7)
  • Coast Fork Willamette to Cottage Grove Dam (approximately river mile 30)
  • Row River to Dorena Dam (approximately river mile 7.5)
The project schedule for all replacement temperature TMDLs is online. To stay informed of this possible schedule change and other project related information, please sign up for email updates on our main TMDL Replacement Project page

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.

Webinar - Jan. 31, 2023

DEQ provided an informational webinar about the Temperature Total Maximum Daily Load Replacements for the Lower Columbia-Sandy Subbasin and the Willamette Subbasins on Jan. 31, 2023. The webinar provided information about the rulemakings and the technical approach to revising the TMDLs and the Water Quality Management Plans.

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A Total Maximum Daily Load is a water quality restoration plan and the calculation of the maximum amount of a pollutant that a waterbody can receive while still meeting water quality standards for that particular pollutant. The maximum amount of loading a waterbody can receive is called the loading capacity. Loading from all pollutant sources must not exceed the loading capacity of a waterbody, including an appropriate margin of safety.

The temperature TMDLs for the Willamette Subbasins will be developed in two phases. The first phase will address temperature listings for waterbodies upstream of the U.S. Army Corps of Engineers dams, as well as PGE's River Mill dam on the Clackamas River. The second Willamette project phase will include the mainstem Willamette River and all the major tributaries downstream of the dams. The exact extents are described in the Quality Assurance Projects Plans listed below. The TMDL phasing considers the extent of the water quality models being used to support the TMDLs, requirements of the court order, and DEQ's available resources.

Quality Assurance Project Plans: Willamette Subbasins

A Quality Assurance Project Plan is developed prior to writing the TMDL and does the following:

  • Define the issue and objectives of the TMDL, including the spatial and temporal extents of the water quality impairments. 
  • Provide a high-level description of the key processes and variables for temperature
  • Outlines the overarching technical approach for the TMDL, including the appropriate modeling and analytical tools to be used.
  • Provides the data sources for defining and creating inputs to the models, including data that were used in the modeling for the original TMDLs, if an original exists. Examples of these inputs can include meteorological data, stream flow and temperature, point sources and vegetation characteristics
  • Describes how the analysis and modeling will be evaluated for acceptability
  • Describes potential scenarios for evaluating management strategies for reducing anthropogenic thermal loads
  • Provides various aspects for managing the TMDL development project, including documentation, the project team, data, and records management

The Quality Assurance Project Plans listed below summarizes the modeling and analysis approach to be used for the replacement temperature TMDLs in the Willamette Subbasins project area. 

  • Southern Willamette QAPP
    Includes the Coast Fork Willamette Subbasin (17090002), the McKenzie Subbasin (17090004), the Middle Fork Willamette Subbasin (17090001), and the Upper Willamette Subbasin (17090003).
  • Middle Willamette QAPP
    Includes the Middle Willamette Subbasin (17090007), the Molalla-Pudding Subbasin (17090009), the North Santiam Subbasin (17090005), and the South Santiam Subbasin (17090006).


TMDL development and implementation is a public process. DEQ will develop 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 rulemaking
DEQ will hold two rule advisory committee meetings and a public hearing. DEQ will present the draft TMDL and Water Quality Management Plan to the Environmental Quality Commission, DEQ's formal policy and rulemaking body, for adoption in November 2023 before submitting the TMDL to EPA for approval or disapproval.

Please visit the rulemaking web page for rule advisory committee meeting dates and information, draft project documents including the TMDL, Water Quality Management Plan, Technical Support Document, and Fiscal Impact Statement, and to sign up for email updates.