Total Maximum Daily Loads


DEQ works closely with local, state and federal agencies as well as the public to improve water quality in the Columbia River and its tributaries. The U.S. Environmental Protection Agency identifies the Columbia as one of the nation’s seven “great water bodies” in need of heightened protection from environmental harm.

DEQ oversees several Total Maximum Daily Load plans to help reduce pollution and toxics in the Columbia. TMDLs calculate the maximum amount of a pollutant that a water body can receive and still meet water quality standards.

Total dissolved gas standard modification for four Columbia River dams

DEQ is seeking public comment on the draft Oregon Environmental Quality Commission order proposing a temporary modification to the 110 percent total dissolved gas water quality standard for the mainstem Columbia River. An approved standard modification will allow the U.S. Army Corps of Engineers to allow voluntary spill to assist juvenile salmonid migration past four lower Columbia River dams: McNary, John Day, The Dalles and Bonneville. The public comment period is from Nov. 6 to Dec. 6, 2019. The following documents about this proposed standard modification are available:

Public hearing

DEQ will hold a public hearing on Dec. 4 on the draft order for the proposed total dissolved gas modification. You can attend in person or via the webinar to learn about the proposed modification, ask questions and provide verbal or written comments on the proposed modification.
Wednesday, Dec. 4, 2019, 6 p.m.
Oregon DEQ Headquarters
700 NE Multnomah St.
3rd Floor Conference Room
Portland, OR 97232

Meeting number: 8774029753
Code: 898168
For webinar audio and to provide comment remotely, dial the meeting number and enter the above code.
The most recent EQC order issued to the U.S. Army Corps of Engineers for modification of the total dissolved gas standard was in effect from 2015 through 2019 for juvenile salmonid migration from Apr. 1 through Aug. 31.


Lower Mid-Columbia River ecological assessment

DEQ completed its “snapshot” ecological assessment of the Lower Mid-Columbia River, which covers 150 miles between Bonneville Dam on the west and McNary Dam on the east. This study –- the first of its kind on this section of the Columbia -- showed that while the river’s fish and bank habitat is degraded, its water quality is generally good, with low levels of metals and organic compounds known as polyacromatic hyrdrocarbons. Unfortunately, bass and largescale sucker fish fillets sampled from the river as part of this study show accumulation of potentially harmful levels of mercury, chlorinated pesticides and other toxic or cancer-causing chemicals, including dioxins, furans, and PCBs.

This assessment fills information gaps and compliments studies conducted by states, tribes, federal agencies and non-governmental organizations to gauge conditions, identify problems and find solutions to pollution issues affecting the Columbia River. The U.S. Environmental Protection Agency listed the Columbia Basin as one of seven Great Water Bodies deserving of special attention and protection from environmental harm.

Total Dissolved Gas TMDL - Lower Columbia River

EPA approved this TMDL on Nov. 18, 2002 

Dioxin Discharges TMDL - Columbia River (as well as Snake and Willamette Rivers)

EPA approved this TMDL, which covers three key waterways in Oregon, TMDL approved by the Environmental Protection Agency on Feb. 25, 1991



Columbia River Basin Coordinator
Paula Calvert,  503-229-5101