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The Duwamish has been a center of Seattle’s growth since the late 1800s when the winding river was straightened into a shipping channel to better support industry.

Development helped the region grow and flourish, but polluted the river with industrial waste, stormwater runoff and overflows of raw sewage during heavy rains.

In 2001, the U.S. Environmental Protection Agency (EPA) classified the Duwamish as a Superfund pollution site . Superfund is a program that finds and requires clean up of contaminated areas that are unsafe for people and the environment. While King County is working closely with the Superfund program, we are also doing additional work to restore the Duwamish.

Cleanup overview

King County and its partners are already making great progress towards cleaning up the river through early action projects. In 2004, King County successfully removed 66,000 cubic yards of contaminated sediment from the river as part of the Duwamish Diagonal cleanup.

City of Seattle just completed the cleanup of Slip 4. Boeing is doing associated cleanup and habitat restoration work. Port of Seattle is cleaning up the Terminal 117 site. These actions will address half of the historical contamination in the waterway. Superfund will address what's left.

Superfund cleanup timeline

Lower Duwamish Waterway Group (LDWG) formed 2000
Superfund listing 2001
Initial assessments made 2000-2003
Remedial Investigation 2003-2010
Feasibility Study 2007-2012
EPA proposes cleanup plan 2013
EPA cleanup decision 2014
Pre-Design work by LDWG  2014-2019 
Negotiate Consent Decree 2018-2019
Cleanup design  2019-2023 
Cleanup activities begin (estimate) 2023
Full cleanup complete (estimate) 2030

The County has worked for decades to restore the waterway by investing in habitat restoration, water quality improvement, pollution controls and sediment cleanups. Learn more.

Who is in charge of the cleanup?

U.S. Environmental Protection Agency and the Washington State Department of Ecology are in charge, but we can all get involved. This includes King County.

Pollutants of Concern

PCBs and other carcinogens
Oil and hydrocarbons
Heavy metals including mercury
Poisons including dioxin, pesticides and arsenic
Stormwater runoff

Duwamish Waterway, circa 1920s
Duwamish Waterway today, looking North
Public information display near Terminal 5, Duwamish Waterway

Your role to clean up the Duwamish

How can I help the Duwamish?Everybody has a role to play in cleaning up the Duwamish and keeping it clean. Visit “How can I help the Duwamish” to find out how your everyday actions can impact our Duwamish.

For more information

For more information about the Duwamish environmental cleanup process, please contact Caryn Sengupta.

Our Duwamish FlyoverFly over the Duwamish River and see King County’s major facilities and services