Protecting Lower Duwamish Waterway

Learn how SPU is keeping pollution out of the Duwamish River.


The Lower Duwamish Waterway (LDW) remains a treasure for the Seattle area despite a legacy of pollution. Once a meandering river, the LDW was dredged and straightened in the late 1800s to make way for large shipping vessels. Decades of polluting industry along its banks left significant contamination in the mud of the waterway and along its banks.

Today the LDW is a major shipping route for cargo, generates significant jobs, provides a recreational playground and remains an important habitat for marine life.

In 2001, The United States Environmental Protection Agency (EPA) listed a 5.5 mile stretch of the LDW as a Superfund cleanup site – meaning, it is among the most polluted sites in the nation. The pollutants of most concern include metals, PCBs (polychlorinated biphenyls) PAHs (polycyclic aromatic hydrocarbons) and phthalates (plasticizers).


View the steps of our pollution source control program.

Lower Duwamish Pollution Source Control Program

The City has an aggressive source control program to keep pollution from entering the LDW. It focuses on three elements:

  • Business inspections 
  • Source tracing
  • Pipe cleaning

These elements are described in detail below.

Business Inspections

The City inspects and works with businesses to ensure that they are using best management practices to keep pollution out of storm drains that flow to the LDW. The inspections address focus on stormwater pollution prevention and also look at issues involving hazardous materials and industrial waste management. The City prioritizes businesses with the most potential for pollution and uses its progressive enforcement program to ensure compliance.

Source Tracing/Characterization Sampling

The City’s source tracing program is designed to identify sources of pollution by collecting sediment samples in catch basins and pipes at key locations within the drainage/combined sewer service areas. When elevated levels of contaminants are found, additional sampling and inspections are conducted upstream to locate the source. Some of the pollutants looked for include metals (arsenic, copper, lead, mercury, and zinc), semi-volatile organic compounds, PCBs, and total petroleum hydrocarbons.

Pipe Cleaning

The City’s storm drain system transports stormwater, but also picks up pollution along the way. When SPU finds high levels of pollution in storm drain sediment, it jets and cleans the pipes to remove the sediment and stop pollution from reaching the waterway. Material removed from the pipe is collected, dewatered, and shipped offsite for disposal. The pipe is then checked periodically to see whether the contamination comes back. If it does, the whole process starts over again with more sampling and business inspections to find and control the source.

SPU works with businesses in the LDW and is aggressively tracing sources of pollution to prevent it from reaching the waterway, but everyone can make a difference in the health of our watersheds.

You Can Help Keep Pollution Out of the Lower Duwamish Waterway

We can all work together to protect the LDW. Take advantage of the following services SPU provides to residents to help protect the Duwamish:

Learn about the City’s efforts to clean up the LDW with project partners

The Lower Duwamish Waterway Group (LDWG) is a public-private partnership that consists of the City of Seattle, King County, Port of Seattle, and the Boeing Company.

The City’s pollution detective work is part of a greater effort by the Source Control Work Group (SCWG) to keep pollution out of the LDW. Led by the Washington Department of Ecology, members of the SCWG include U.S. EPA, City of Seattle, King County, and the Port of Seattle.


Source Control Implementation Plan

The City has completed a Draft Source Control Implementation Plan (SCIP). The Washington Department of Ecology is modifying the Phase I Municipal Stormwater Permit to incorporate the actions of the SCIP into the Permit. The Washington Department of Ecology is holding a public comment period for this action. More information can be found on the Washington Department of Ecology’s website.

The Source Control Implementation Plan Documents are available for review:

Other Documents:

View earlier progress reports:

Learn more about pollution source control or how to report a problem.