Skip to main content
King County logo

Health and environment

The Lower Duwamish Waterway is a working river that has supported Seattle’s economy for more than 100 years. Most of the pollution comes from past industrial practices and development decisions that would no longer be permitted today. These practices allowed contaminants to enter the waterway and settle into the sediment in the bottom of the river. The U.S. Environmental Protection Agency, or EPA, listed the river as a federal Superfund cleanup site in 2001 to address this historical pollution in the river sediment.
Studies have found a variety of chemicals including heavy metals, oil, industrial waste and sewage. The biggest chemicals of concern are polychlorinated biphenyls, or PCBs, which have been banned since the 1970s. PCBs are linked to cancer. Other toxins include arsenic and dioxins. PCBs, dioxins and arsenic are toxic to people and wildlife.
Like all other urban waterways, the biggest ongoing source of pollution in the Duwamish today comes  from stormwater runoff that carries chemicals from our cars, buildings, roads, businesses and yards. King County is working with the City of Seattle and the State Department of Ecology to find ways to control these sources of pollution.

Warning SignThe Washington State Department of Health has warned people not to eat crab, shellfish or certain kinds of fish from the Lower Duwamish. Salmon are safer because they migrate through the river and don’t spend most of their lives in there.

Fish and shellfish in the Duwamish became contaminated because they live and eat there, which exposes them to pollution in the river sediment. Cooking doesn’t remove the toxins. Eating contaminated seafood is especially dangerous for children, nursing mothers and pregnant women.

Fish advisories are not uncommon in highly populated urban areas. There are also fish warnings in Lake Washington, Green Lake, and Puget Sound.

King County wants to make sure people know how to reduce their risk of exposure to dangerous pollutants and toxins by avoiding unsafe seafood . This information is available in Spanish ; Vietnamese ; Cambodian ; Hmong ; Laotian ; Chinese ; and Russian .

Combined Sewer Overflow Warning SignPeople can swim in the river, but be aware that there are areas where combined sewer overflows (also known as CSOs) may discharge stormwater and wastewater into the waterway during storms. These areas are marked with signs.

King County cautions people against swimming or fishing near combined sewer overflows for at least two days (48 hours) after the last heavy rain where a CSO has discharged. This website offers real-time updates where CSOs might be happening in the Seattle area.

King County's CSO control plans include significant investments in the Lower Duwamish.

According to the Washington State Department of Health, the main pathway of exposure to toxins in the waterway comes from eating fish and shellfish that spend most of their lives in the river.

Though it is considered safe to play in most public areas, such as Duwamish Waterway Park, people could still face health risks by coming into direct and repeated contact with contaminated sediment in some areas of the river. Taking simple steps can reduce the risk of exposure to these toxins.

After playing in the river or along the bank:

  • Wash your hands and face with soap afterwards, especially before eating.
  • Clean dirt from under your nails.
  • Wash soiled clothing separately.
  • Wash your children's hands, toys, and pacifiers -- young children are especially sensitive to contaminants.
  • Keep pets clean.

In 2014, EPA decided on their cleanup plan for the Duwamish. The Lower Duwamish Waterway Group (LDWG), a partnership between King County, the Port of Seattle, City of Seattle and The Boeing Company, has been actively cleaning up waterway pollution. These investments of nearly $200 million on studies and cleanup of early action areas will reduce contamination, such as Polychlorinated biphenyls (PCBs), found in the waterway:

  • Enhanced Natural Recovery Activated Carbon Pilot Study - conducting a pilot study with an innovative sediment cleanup technology. Learn more .
  • Fishers Study - completed a study in partnership with the US Environmental Protection Agency (EPA) and the Washington State Department of Ecology (Ecology) to learn more about fishing on the Lower Duwamish Waterway. Learn more .
  • Pre-Design Studies - working with the EPA on pre-design studies to inform the cleanup. Learn more .

But King County’s environmental commitments in the Lower Duwamish go far beyond Superfund cleanup.

One of the biggest efforts involves controlling combined sewer overflows (CSOs) occur in older parts of Seattle where pipes were once designed to carry both sewage and stormwater fill to capacity during heavy rain. There are five locations where CSOs occur in the Lower Duwamish, and King County has a plan to invest in controlling these overflows.

King County is also working with other agencies to keep the river clean by controlling other sources of pollution .

Superfund cleanup

Superfund is the common name for areas determined by the federal government to be so contaminated by toxic chemicals that they must be cleaned up to protect both human and environmental health.

In 2001, the U.S. Environmental Protection Agency listed a five-mile segment of the Lower Duwamish south of the West Seattle Bridge as a federal Superfund cleanup site due to the presence of historically contaminated sediment in the bottom of the river.

King County operates a regional wastewater treatment system as well as the King County International Airport, also known as Boeing Field. King County also owns property leased to small businesses and industries.These facilities contributed to the historical pollution because prior to today's pollution control practices, they discharged stormwater runoff or overflows of stormwater and wastewater into the waterway during heavy rains. The stormwater and sewage contained contaminants that settled into the sediment at the bottom of the river.

There are many other companies, businesses and local governments, known as “potentially responsible parties”, or PRPs, that also contributed to the historical pollution.

Cleanup is the right thing to do for the region and our residents. Before the Superfund listing in 2001, King County joined with the City of Seattle, the Port of Seattle, and Boeing, to form the Lower Duwamish Waterway Group, or LDWG. The group has been proactively working with the EPA and the Washington State Department of Ecology to get the cleanup started.

King County and its Lower Duwamish Waterway Group partners believe that the sooner cleanup begins and the quicker it’s completed, the better it is for everyone -- the people who live and work nearby as well as the fish and wildlife habitat that live in the river.

There have been many studies about the best way to clean up the river. All of the methods come with varying costs and impacts to the people who live and work nearby. The cleanup has to meet certain standards, so a cleanup that costs more or takes longer won’t reduce risks or make the river cleaner.

While the EPA has listed the entire five-mile waterway as a Superfund site, toxins are more concentrated in certain areas we call “hot spots”. Dredging, which entails digging up and disposing of contaminated mud in a landfill, is best targeted to only the “hot spots” where the benefits of this method would outweigh the community impacts and construction-related risk.

Areas with lower levels of pollution can be isolated by treating with activated carbon, which takes up and holds onto toxins and keeps them out of the organisms and fish in the river. Another technique, called “capping”, can be used in areas with low to moderate levels of pollution. Capping entails covering polluted areas with clean sand so organisms can't be exposed to contaminated mud.

Areas with very low levels of contamination are best allowed to “naturally recover”, a normal ecological process in which clean, healthy sediment deposits from upstream cover the river bottom over time. King County and others would regularly monitor this natural recovery process for many years. If natural recovery wasn’t working, or wasn’t working as expected, these areas could be treated or dredged.

Under this approach, the cleanup construction could be completed in under 10 years. A faster, safer cleanup would benefit the community years earlier than other approaches that take longer, cost more, and reach the same cleanup outcome.

One cleanup approach we studied includes extensive dredging – basically, digging up the sediment on the river bottom and disposing of it in a landfill. Though some people think this is a good approach,  there are many problems with it.

First, dredging is dangerous because it stirs up chemicals currently buried and isolated in the mud at the bottom of the river. In “hot spots”, the benefits of targeted dredging outweigh the risk. However, a large-scale dredging project would last for decades and stir up contaminated mud and pollute the water with harmful chemicals, increasing health risks to people who swim and fish.

Dredging also requires the use of heavy equipment and large trucks or train cars to haul dredged material to disposal sites. This would increase traffic and air pollution in areas that already have high asthma rates. It's also important to consider that dredged sediment would need to be hauled to another community, creating additional environmental and community impacts.

Finally, extensive dredging would take up to 40 years, forcing residents and workers to endure decades of increased health risk, inconvenience and reduced quality of life for no additional benefit.

According to a National Academy of Sciences study from 2007 dredging alone isn’t always an effective cleanup method. This study found the most successful cleanups are done using more than one method.

Under Superfund laws, cleanup costs are paid for by businesses and public agencies found by EPA to be responsible for the historical pollution. There are no federal funds to pay for Superfund cleanup.

King County and other public agencies will pass along their share of cleanup to costs to the people who pay taxes and sewer utility bills. Private companies will need to factor cleanup costs into their business costs. It’s important to consider the impact cost will have on people in the region.

The cleanup alternatives being proposed range in cost from $200 million to $1.3 billion. Regardless of which alternative is selected, cleanup must meet the same level of risk reduction, so spending more money doesn’t mean the river will be cleaner or safer.

Over the past decade, King County and its LDWG partners have invested $40 million studying cleanup approaches and $80 million on Early Action cleanups that will reduce pollution levels by up to 50 percent before Superfund cleanup even gets started.

In 2004, King County completed a sediment cleanup and removed 66,000 cubic yards of sediment from the river.

These projects are already making a positive impact on the river health and ecology.

EPA issued the Record of Decision - or "ROD" - in 2014. The ROD is the EPA’s cleanup plan to reduce risks to people’s health and the environment from toxic chemicals in the river. Learn more by visiting EPA's Lower Duwamish Waterway Superfund Site .

King County programs and services

King County government is a major property owner and a service provider in the Lower Duwamish area. We manage transit service, wastewater facilities, trails, health services, roads and bridges, and even an international airport.

Our agencies are dedicated to enhancing the quality of life and protecting public health and the environment. We are proud to be both part of the community and a representative to the people who live and work there.

Business and jobs

Superfund cleanup will have a big influence on our regional economy. Whether it helps or hurts depends on how it proceeds.

Businesses know the cleanup is coming and they want the process to be fair and reasonable. If it’s not, there’s a greater chance of legal disputes that will delay the cleanup and cause businesses to relocate elsewhere.

Superfund cleanup conflicts have had a chilling effect on the economy in other areas, including the Portland Harbor Superfund Site in Oregon. Commercial and industrial activity in the Lower Duwamish accounts for 8 percent of King County’s total employment, so this is a real concern.

King County believes a reasonable and fair approach to cleanup has the best chance of moving forward. A cleaner river has the potential to attract more business and investment to the area, and we’re eager to get started.

Because the cleanup is required to meet the EPA’s environmental standards, a reasonable approach doesn’t let businesses “off the hook” or allow them to do a lower level of cleanup.

The Lower Duwamish is an economic engine area that supports more than 100,000 jobs, which is 8 percent of King County’s total employment. Many of these jobs pay good wages without requiring advanced education, and the companies located in the area depend on access to major rail lines, freeways and port facilities.

The total value of the goods and services produced in the Lower Duwamish industrial area averages $13.5 billion annualy. The economic activity supports many jobs in the region, even those outside the immediate industrial area.

The industrial area is vital to our economy and King County wants to make sure it remains a good place to retain and grow commercial and industrial businesses.

Because of stringent environmental laws, industries are no longer permitted to discharge industrial process water directly to the river. The biggest source of pollution in our waterways today comes from stormwater runoff from streets, parking lots, homes and commercial/industrial businesses.

As we clean up historical pollution from decades ago, King County is also working with the Department of Ecology and City of Seattle to to keep new and ongoing sources of pollution out of the river.

At very most, cleanup work is forecast to create fewer than 1,000 seasonal jobs, most of which would be based outside the Lower Duwamish Waterway area. Cleanups with more dredging would actually have more jobs located outside the area due to the need to haul and dispose of dredged mud at distant landfills.

The industries and businesses currently in the Duwamish industrial area will continue to be the primary source of jobs for the local community.


The Lower Duwamish is mainly an industrial area, but it’s also home to some of Seattle’s most wonderfully diverse communities. An estimated 5,000 people live in neighborhoods near the Lower Duwamish. A large percentage of community members are immigrants or speak another language besides English at home.

King County recognizes that many people in Lower Duwamish communities live with many stresses, such as poverty and poor air quality. There are higher rates of disease, such as diabetes or asthma. Some neighborhoods have few transit options, shops or parks. Fixing these inequities is a big job, and it goes beyond environmental cleanup work. King County can’t solve these problems alone, so we’re working with other agencies and community groups to find ways to remove barriers that limit opportunity and the ability of people to achieve their full potential.

Equity and social justice means treating all people fairly while creating stronger and healthier communities together. King County government recently passed a law that requires equity and social justice to be reflected in policy making so that all community members have access to the same opportunities and levels of service. The principles of equity and social justice are a major factor in how King County serves and communicates with people who live and work in Lower Duwamish neighborhoods.

When it comes to Lower Duwamish cleanup, equity and social justice is also a consideration for people and communities outside the area that may experience impacts of cleanup decisions, such as those near landfills.

Superfund cleanup will ultimately have a very positive effect on nearby communities. A successful cleanup will likely attract more business and investment in the area, and it will improve water quality for people, fish and wildlife.

However, people should expect construction-related impacts while cleanup is under way, including increased truck traffic, equipment noise, exhaust emissions, and an increase in water pollution levels during dredging. How long these impacts last depends on how long it takes to complete Superfund cleanup.

King County supports a Superfund cleanup that will meet EPA’s cleanup standards with fewer than 10 years of construction. Other cleanup alternatives take up to 40 years, cost more money, and don’t get the river cleaner.

How the cleanup is carried out is important. A cleanup with extensive dredging would mean years of impacts for people who live and work nearby. It would also burden people in communities that host the landfills where the dredged mud must be hauled for disposal.

All of us can do something to keep our waterways clean and healthy. Here are some simple tips that can make a big difference.


Frequently asked questions and other information on the Our Duwamish web pages have been translated into SpanishVietnamese and Somali.

Spanish Vietnam Somali

For more information

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

Postcard: How will the Duwamish Environmental Cleanup impact me? (PDF), July 2012,
See also: postcard to businesses (PDF), July 2012