DEQ and the EPA worked together to revise the 2006 Willamette Basin Mercury TMDL 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 waterways. Among those who rely on Willamette Basin fish and shellfish as a food source are tribal, immigrant and low-income communities and other historically marginalized communities.
Water quality standards are in place to protect people from high levels of mercury exposure when eating fish and shellfish. The Willamette River and many of its tributaries do not currently meet water quality standards for mercury and are included on Oregon's list of impaired waters under Clean Water Act §303(d). Mercury fish consumption advisories are in place throughout the Willamette Basin.
The TMDL identified sources of mercury and how much mercury needs to be reduced to meet water quality standards. The TMDL used linked models and significantly more data than the 2006 TMDL. The greatest source of mercury in the basin is from atmospheric deposition, which is mercury in the air falling onto the land or into the water. The mercury in air originates mainly from national and global sources rather than from sources in Oregon.
Once mercury is deposited on the landscape, the major pathways to streams are erosion of sediment-bound mercury and surface runoff. Of the many different types of land use that exist within the Willamette Basin, forestry, agriculture and urban uses comprise most of the area within the basin. Management actions on these land uses influence the amount of mercury from these sources that reach streams and rivers in the basin. Point source discharges, such as sewage treatment plants or industries, contribute significantly less mercury to streams than nonpoint sources, such as runoff from logging roads and agricultural fields.
The water quality management plan describes DEQ's plan for implementing actions to reduce mercury in fish tissue. Mercury minimization measures will be applied for both point and nonpoint source activities, with primary focus on reducing runoff and erosion from nonpoint source activities and urban stormwater. Effectiveness of these measures will be tracked, evaluated and improved, as warranted, to meet the standards.