Total Maximum Daily Loads

Title: Revised Willamette Basin Mercury
Water Quality Limited Parameters: Mercury
Pollutants: Methylmercury and Total Mercury
Status: EPA Disapproved Nov. 29, 2019, EPA Issued TMDL Dec. 30, 2019

Project summary

In Sept. 2006, EPA approved DEQ’s mercury TMDL for the entire Willamette Basin. DEQ developed the TMDL to meet a mercury target in place at the time. Northwest Environmental Advocates filed a lawsuit in 2012, which argued the validity of the mercury TMDL and EPA’s approval of the TMDL. In April 2017, the US District Court issued a ruling requiring EPA to revise the TMDL by April 2019, and allowing the 2006 TMDL to remain in effect until EPA issues or approves the revised TMDL. The court has since approved a DEQ and EPA extension request to Nov. 29, 2019.

Current actions

Dec. 30, 2019

EPA established the Willamette Basin Mercury TMDL. EPA will open a public comment period for this TMDL from Jan. 6, 2020 through Feb. 4, 2020. EPA’s TMDL used some of Oregon’s 2019 TMDL, with the major changes being revisions of some of the load and wasteload allocations. Additional information about EPA’s public comment period will be posted by EPA on Jan. 6, 2020.

November 2019

Oregon DEQ and the U.S. Environmental Protection Agency are working together to revise the 2006 Willamette Basin Mercury Total Maximum Daily Load to meet the fish tissue methylmercury criterion adopted in 2011. This criterion allows Oregonians to safely consume higher amounts of fish (Approximately 23 8-oz fish meals a month) caught in Oregon's waterways.

DEQ issued the Revised Willamette Basin Mercury TMDL on Nov. 22, 2019. On Nov. 29, 2019, EPA disapproved the TMDL). Under the Clean Water Act and implementing federal regulations, EPA has establish a new TMDL.

Project documents

For requesting data, models or other information used in this TMDL, please complete a "Public Records Request".

Advisory committee meetings

Public hearing and request for comments

Fact Sheet


Monitoring Strategy




Willamette Basin Coordinators

Basin Coordinator List

Watershed Management Manager
Gene Foster 503-229-5325

Other TMDLs in the Willamette Basin

Make a Public Records Request