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Duwamish River Superfund Site

Duwamish River Superfund Site

How it got polluted and what's being done to clean it up

The last five miles of the Duwamish River towards Elliott Bay is one of the most polluted rivers in the country! In 2001, the US Environmental Protection Agency (EPA) declared it the Lower Duwamish Waterway Superfund Site. Superfund is the name of a federal law that requires the nation’s most toxic sites to be identified and cleaned up.

The EPA and Washington Department of Ecology (Ecology) are overseeing the cleanup of this site. Dozens of Potentially Responsible Parties (PRPs) will be required to pay for the cleanup.

The main agencies involved in protecting public health and cleaning up the site are:

  • EPA leads the cleanup of the contaminated mud of the river bottom at the site.

  • Ecology leads efforts to control chemical pollution from getting into the Duwamish River from the surrounding area.

  • Public Health — Seattle & King County leads the Fun to Catch, Toxic to Eat program for EPA to promote safe seafood consumption for the Duwamish River Superfund Site.

The Duwamish River connects from the Green River in Tukwila. The Duwamish River flows past the South Seattle neighborhoods of Georgetown and South Park, through Seattle’s industrial core, under the West Seattle Bridge and then empties into Elliott Bay.

The Duwamish River is a place you can catch freshwater fish and saltwater fish. The Spokane Street Bridge is at the mouth of the Duwamish River and is one of the most popular fishing sites along the river.

The Duwamish River is Seattle's only river and may be called by other names, such as "Spokane Street Bridge fishing site", "Southwest Bridge fishing site", "the river near South Park", or "the river that is near or goes under West Seattle Bridge".

Chemical pollution gets into our environment from many sources. You cannot see, smell or taste most of the chemical pollution that gets into the water, mud and fish. For over a century, the Duwamish River became polluted with toxic chemicals from many sources, including storm water runoff, wastewater, and industrial practices.

The toxic chemicals in the Duwamish River that are most dangerous to people’s health are polychlorinated biphenyls (PCBs), arsenic, carcinogenic polycyclic aromatic hydrocarbons (cPAHs), dioxins and furans.

These toxic chemicals build up in the mud of the river and get into the flatfish (perch, sole, flounder), crab, mussels and clams that spend their entire lives in the river. They are called "resident seafood". Regularly eating resident seafood from the river can increase your chance for health problems later on. Contact with the contaminated mud also poses a health risk.

The only Duwamish seafood safe to eat is salmon
because they spend a short time in the river.

How contaminants (like PCBs) from the Lower Duwamish River build up in humans
  1. Contaminants (like PCBs) get into the water and flow into the Duwamish River. Some contaminants stick to the sediment (mud) and end up staying on the bottom of the river.

  2. Microscopic animals (zooplankton), worms, and mussels live in the sediment and contaminants get into their bodies.

  3. Larger organisms, like Shiner perch, English sole and crabs, eat the bottom-dwellers and store even more contaminants in their bodies.

  4. Humans may catch and eat the contaminated fish and crab. The more seafood that a person eats, the more contaminants may be stored in his/her body which may affect his/her health.

Illustration of how contaminants get in fish in the Lower Duwamish River.

The EPA leads the cleanup of the contaminated mud of the river bottom at the Lower Duwamish Waterway Superfund Site. Like other complex Superfund sites, the Duwamish River Superfund Site has multiple phases.

  • Over the past years, the City of Seattle, King County, the Port of Seattle, and the Boeing Company, joined together as the Lower Duwamish Waterway Group (LDWG) to clean up some of the most polluted spots along the river. EPA and Ecology oversaw their early cleanup work, and found that this early cleanup reduced the PCB contamination in the river bottom by approximately half.

  • In 2014, the EPA issued a Final Cleanup Plan, also known as a "Record of Decision (ROD)", for cleaning up the remaining contaminated mud on the river bottom. This will further reduce risks to people's health and the environment from toxic chemicals in the river.

    The Plan requires both active and passive cleanup measures, like:
    • Dredging (removing the toxic mud)
    • Capping (covering the river bottom with a thick layer of clean dirt), and
    • Enhanced Natural Recovery (covering the river bottom with a thinner layer of clean dirt)

  • The Plan also calls for Monitored Natural Recovery (natural sedimentation) in some areas.



Enhanced natural recovery
Monitored natural recovery

Public Health's community-based health outreach program is part of the EPA's Final Cleanup Plan to protect people who fish and eat the resident seafood.

Over the coming years, the EPA will oversee the design and cleanup of the remaining contaminated mud. The EPA will monitor and maintain the site over time. As cleanup and source control continue, testing will be repeated to assess progress towards long-term cleanup goals.

EPA Duwamish River cleanup timeline

Timeline acronyms
AOC Administrative Order on Consent  
MTCA Model Toxics Control Act  
RA Remedial Action  
RD Remedial Design  

More information: EPA's Lower Duwamish Waterway Superfund Site website.

The EPA provides various opportunities for communities to give input into the cleanup. The EPA takes into account Environmental Justice (EJ), meaning it will aim to ensure the fair treatment and meaningful involvement of all people regardless of race, color, national origin or income.

The EPA's Community Involvement Plan provides an overview on the engagement tools and techniques that the EPA will use throughout the cleanup of the LDW Superfund Site.

One of these opportunities for communities to get involved is with the Duwamish Roundtable. This group is made up of interested parties who will provide recommendations to EPA for the design and implementation of the cleanup.

If you would like to become a member of the Roundtable or are interested in attending one of the Roundtable meetings, please contact Julie Congdon at 206-553-2752 or

For more information on how to stay updated and get involved in the Superfund cleanup, please visit EPA's Duwamish Community Involvement website, EPA's Duwamish Cleanup Facebook, or Duwamish River Cleanup Coalition page.

Ecology is leading efforts to control sources of chemical pollution from getting into the Duwamish River from the surrounding area. There are 20,000 acres of land that drains into the river. Toxic chemicals in the soil and groundwater from this surrounding area can find their way into the river through storm runoff and other routes.

Contaminant sources

Source control means finding the sources and extent of chemical pollution, then taking actions to stop or reduce them before they reach the river. Source control actions include:

  • investigation and cleanup of contaminated sites,
  • business inspections,
  • controlling storm water runoff and combined sewer overflows,
  • coordination among agencies, and
  • education

Thanks to source control, early cleanup actions, and natural sedimentation, the Duwamish is less polluted than it used to be. As Ecology further controls sources of pollution to the river, the risk that the sediments will become polluted again (recontaminated) will be low enough. EPA will move forward with phased cleanup of remaining areas of contaminated mud on the river bottom. In the long-term, EPA will monitor the natural recovery of the river and Ecology will continue to reduce pollution sources. These actions will help the river get as clean as possible and make seafood safer to eat.

More information: Ecology's Lower Duwamish Waterway Source Control Program website.