TMDL image

Water Quality Improvement Projects (TMDLs)

Water Quality Improvement Projects
Chehalis River Basin Area


The Chehalis River Basin (Basin) is located in western Washington State between the Deschutes River Basin to the east, the Cowlitz River Basin to the south, the Willapa Hills to the southwest, and the Olympic National Forest to the north. The Basin includes parts of Lewis, Thurston, Pacific, Grays Harbor, and Mason counties.

The Basin is the second largest river basin in the state (the largest is the Columbia River Basin), with a total drainage area of the Basin is 2,660 square miles.

The majority land use within the Basin is forestry, including private commercial forest lands as well as publicly-owned forest lands in the Olympic National Forest, Capitol State Forest, and Mt. Baker-Snoqualmie National Forest. A variety of crop and livestock agricultural land uses constitute approximately 8% of the basin and are also a significant economic driver. Commercial and recreational shellfish harvesting is also important to the Grays Harbor area.

The Confederated Tribes of the Chehalis Reservation is somewhat centrally located in the Chehalis River watershed, near the town of Rochester. The Quinault Indian Nation has treaty rights to protect their usual and accustomed areas within the Basin, while their reservation is contained within Jefferson County along the coast.

The four major population centers: Chehalis, Centralia, Aberdeen, and Hoquiam depend on groundwater and surface waters of the basin for the largest portion of their municipal and industrial supplies. The Port of Grays Harbor is located in Aberdeen. Shellfish harvesting depends on receiving good water quality from the Chehalis River and other tributaries directly to the harbor. Port activity relies on annual dredging by the Army Corps of Engineers to maintain the navigation channel and turning basin in Grays Harbor.

The resident and anadromous fish resources are of national, local, and international economic significance. Significant anadromous fish species include fall and spring Chinook, Coho, Steelhead Trout, Chum, and Bull trout. Sport, tribal, and commercial fishing are important to the economy of the Basin. The Quinault Indian Nation and the Washington Department of Fish and Wildlife are co-managers of the salmon fishery in this basin. There are many state and private fish hatcheries throughout the basin to support recreational, commercial, and tribal fisheries.

Water quality issues

Development is concentrated in areas close to important streams and rivers, mostly along state and federal highway corridors. Past community development decisions have adversely impacted water quantity and water quality. Forestland management practices also strongly affect water flow and quality in the Basin. Currently there are no listed threatened or endangered salmon populations in water resource inventory areas (WRIAs) 22 and 23, but continued actions to improve salmon habitat and water quality are needed to keep it that way in light of increasing levels of direct anthropogenic impacts. Pollution from most all land types (urban, rural, agricultural, forestland, commercial, industrial) is documented in many Chehalis watershed studies by various organizations. Low dissolved oxygen, higher water temperatures, and bacteria levels are primary water quality concerns.

Total Maximum Daily Load (TMDL) reports have been approved by the U.S. Environmental Protection Agency (EPA) for bacteria, temperature, dissolved oxygen, and dioxin. Please see the Project Information table for specific information about each TMDL project.

What is being done

Various organizations are helping to protect and enhance salmon habitat and improve water quality. A local discussion and water resource planning group called the Chehalis Basin Partnership (CBP) helped develop plans for water quality improvement. Ecology collaborates with the CBP and other watershed stakeholders to improve water quality and reduce non-point sources of pollution, as well as regulating point sources of pollution through National Pollutant Discharge Elimination System (NPDES) permits.

Ecology is also engaged with the Chehalis Salmon Recovery Lead Entity in this watershed. Salmon recovery projects can be more than just correcting or removing fish passage barriers. They can also improve instream and riparian habitat that helps improve water quality. By working together with local stakeholders, the CBP, and salmon recovery groups we approach water quality problems holistically, with multiple perspectives and expertise, to ensure that investments of public money are well spent on solutions that are good for water quality, people, and salmon.

Project information

Water-body Name Parameter(s)
Chehalis River, Upper Dissolved Oxygen
Fecal Coliform Bacteria
Grays Harbor Dioxin
Fecal Coliform Bacteria
Humptulips River Temperature
Simpson Timberlands Temperature
Wildcat Creek Ammonia-N/BOD
Dissolved Oxygen
Fecal Coliform Bacteria


Contact us for more information

Back to top of page


Last updated March 2016