Total Maximum Daily Loads

The Oregon Department of Environmental Quality is convening an advisory committee to develop a revised Willamette Basin Mercury TMDL.


In September 2006, EPA approved DEQ’s mercury TMDL for the entire Willamette Basin. DEQ developed the TMDL to meet a mercury criterion 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.
DEQ and EPA are revising the TMDL to meet Oregon’s current water quality criterion for methylmercury, which is eight times more stringent than the criterion in effect in 2006. EPA approved Oregon’s revisions to its methylmercury fish tissue concentration criterion for the protection of human health in October 2011. The revised criterion changed the acceptable level from 0.3 mg/kg (milligram of methylmercury per kilogram of fish tissue) to a significantly more protective 0.040 mg/kg.

Committee documents


Next meeting

June 13, 2019, 8:45 a.m. - 12:45 p.m.

Executive Building, Conference Room A
155 Cottage St. NE
Salem, Oregon 97301

Past meetings

Friday, April 26, 2019

Meeting 7 Webinar - March 7, 2019

Meeting 6 - Sept. 19, 2018

Meeting 5 - Aug. 22, 2018

Meeting 4 - July 17, 2018

Meeting 3 - March 21, 2018


Meeting 2 - Feb. 15, 2018



Willamette Basin Mercury TMDL advisory committee managers:
Andrea Matzke, 503-229-5350
Priscilla Woolverton, 541-687-7347
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Click for a larger map of the 303(d) listings for mercury in the Willamette Basin.