Total Maximum Daily Loads

The purpose of this website is to let you know about the positive actions being accomplished and undertaken to improve water quality in the Willamette River and its tributaries.

The Willamette River Basin is home to seventy percent of Oregon's population. Those who live or work in the basin depend on the river for many resources, and also contribute to potential pollution problems that come with any residential, municipal, industrial, or agricultural operation.

For the amount of land area in the basin, more water flows from the Willamette River than from any other major river basin in the United States. The basin, 180 miles long and 80 miles wide, is bordered by the crest of the Cascade Mountains to the East, the crest of the Coast Range to the West, and the Columbia River to the North where the two rivers meet. About 2.3 million people live in the river basin near its 16,000 miles of rivers and streams, and more than half of them live in the Portland metropolitan area.

As population increases, and land conversion to urban and industrial uses continues in the basin, these changes affect the Willamette River.

For example, the household chemical products applied in and around the home, including pesticides and fertilizers, may end up in the Willamette after passing through treatment plants or in storm water runoff. Pollutants can reach the river through groundwater as well as from runoff and pipes.

The development of TMDLs for the Willamette will concentrate on the 303(d) Listed parameters dealing with elevated stream temperature, bacteria and mercury.

​Decades of work and millions of dollars of investment by the State, industry, and cities has reversed some of the worst damage to the Willamette River. Cities and industries began treating wastewater in the 1950s, and treatment has improved steadily since. Flood control reservoirs built by the federal government have increased summer flow, providing waste dilution during this critical period. Today the river is cleaner and healthier than it once was for people and fish. However, there is still much work to be done.

The Oregon Plan is a commitment from Oregons citizens, businesses, agencies and governments to work together to ensure our children will inherit healthy watersheds. The Oregon Plan is people working locally; watershed councils coordinating the work; local landowners and governments initiating new ways of doing things; funding and expertise from state, tribal and federal agencies, and businesses and industries; and implementing existing laws and regulations. Most of all, it is a spirit of volunteerism and stewardship characteristic of Oregon and Oregonians.

Efforts to restore the watershed involve everyone in the watershed. Actions include planting vegetation to reduce erosion and keep water cool; changing habits at home, at work, and at play to prevent or reduce pollutants entering waterways; improving fish passage and opening habitat that was blocked by past practices; and reducing erosion and sediment entering streams. For more information on how to help, view Preventing Surface Water Runoff.

Mercury is another key issue that people can learn more about to reduce its impairment on the environment. DEQ is actively involved in a  study to reduce mercury pollution in the Willamette.

TMDLs and Water Quality Management Plans

Oregon is required to establish Total Maximum Daily Loads (TMDLs) for streams segments which do not meet water quality standards. The TMDL identifies the level of pollutants that a water body can absorb and still meet  water quality standards. TMDLs take into account pollution from all sources, including discharges from industry and sewage treatment facilities; runoff from farms, forests and urban areas; and natural sources. TMDLs also include a safety margin to account for uncertainty.

This information is then used to determine what changes must take place to achieve water quality standards. The TMDL will be used to determine whether changes are needed for wastewater discharge permits for industries and sewage treatment facilities. Water quality management plans are also developed based on the TMDLs. These plans document the ways that local landowners, agencies, forest and agricultural land managers (including federal agencies), DEQ and others will implement a specific TMDL and work to improve water quality.

More information on the Willamette

​Willamette Basin

Addendum 1: Modifications to the Willamette Basin Temperature TMDL

Approved by the US Environmental Protection Agency on November 23, 2011

Additional information regarding the Willamette Basin TMDL, including the Willamette Basin Rivers and Streams Assessment.

TMDL approved by the US Environmental Protection Agency on Sept. 29, 2006

Willamette River Basin Temperature TMDL modeling reports from Portland State University and USGS:

Other Documents

Coast Fork Willamette Subbasin

TMDL approved by EPA on May 17, 1996

Columbia Slough Watershed

TMDL approved by EPA on Nov. 25, 1998

Middle Willamette Subbasin

Rickreall Creek

TMDL approved by EPA on April 18, 1994

Molalla-Pudding Subbasin

TMDL approved by EPA on Dec. 31, 2008

Pudding River 

TMDL approved by EPA on Dec. 18, 1993

Tualatin Subbasin

Tualatin Subbasin TMDL Revision Approved by EPA on December 14, 2012

TMDL approved by EPA on August 7, 2001

Yamhill Subbasin

TMDL approved by EPA on March 16, 1992

   TMDL Report In-Progress (Data analysis and report writing phase) - For updated TMDL.