My Basin photo identifier

My Basin

Photo of the upper Green River showing an intact riparian.  Photo courtesy of Tyler H Patterson, Tacoma Water.

Green-Duwamish River Basin


Did you know?

Historically the Duwamish estuary was about 1600 square miles in size and drained the Green, White, Black, and Cedar Rivers. No wonder it was often called the river of many colors!

After a flood in 1906, the White River was diverted to the Puyallup River. In 1909, the lower Duwamish was channeled, deepened, and Harbor Island created to act as a port for the growing industrial engine of Puget Sound. In 1911 flooding on the Cedar River prompted the relocation of the Cedar River outlet from the Black River to Lake Washington and the engineering of Lake Washington to discharge at the Ballard Locks. These actions shaped what we recognize today as the Green-Duwamish watershed.

Lower Green River (Hor5sehoe Bend, Kent). Photo courtesy of Chris Coffin, WA Department of Ecology The Green-Duwamish River originates in the Cascade Mountains and drains to Elliott Bay in the Puget Sound. The large river, 65 miles in length, is called the Green River upstream of Tukwila (River Mile 12) and the Duwamish River downstream to Elliott Bay. Major tributaries to the Green-Duwamish include the Soos and Newaukum creeks.

The watershed is characterized by many land uses including urban development, agricultural production, and native fisheries. The headwaters of the Green River provide drinking water for much of the city of Tacoma. These drinking waters are stored in a reservoir behind the Howard A. Hanson Dam which also provides flood control benefits to the valley downstream. This is especially important for agricultural production in the Green River valley, historically the most fertile and productive agricultural area in the state. Today, the Green River valley is also home to one of the largest warehouse distribution and manufacturing centers in the United States. Much of southern King County, including south Seattle and the suburban areas of Kent, Auburn, Covington, and other cities are in the Green-Duwamish watershed. As a result, the Lower Green and Duwamish river (Green-Duwamish River) is dominated by urban development and high population density. The bottom 5.5 miles of the watershed is known as the Lower Duwamish Waterway.

The Green-Duwamish River is home to many native Chinook, chum, coho and winter steelhead salmon that use the river as a migration corridor when heading to and returning from the ocean. Historically, the Green River fed generations of people with abundant salmon. In fact, because salmon was so abundant, salmon hatcheries were located in the Middle Green tributaries to help bolster this now challenged resource. Many Native American peoples, as well as other local populations rely on salmon for subsistence. Regrettably some of these salmon runs are threatened, endangered, or extinct.

The Washington State Department of Ecology acts under the authority of the Clean Water Act and the state's water quality law to clean up and protect the Green-Duwamish River in an effort to preserve and restore its many diverse water uses. Other state and federal laws play important roles in cleaning up and protecting this watershed. Refer to the Project and Resource Links for information about ongoing environmental protection and resource management activities occurring in Green-Duwamish watershed.

Green-Duwamish basin map.  Developed by Tetra Tech for the WA Department of Ecology.