Lower Duwamish Source Control

The City's program to keep pollution from entering the Lower Duwamish Waterway (LDW) is an important element of the watershed-wide source control strategy led by Ecology. Learn more about Ecology's Source Control Strategy.

The City’s program has three elements: source tracing, business inspections, and pipe cleaning.

Source tracing/characterization sampling

The City collects and tests sediment samples from area catch basins and pipes. When elevated contaminant levels (arsenic, copper, lead, mercury, and zinc, semi-volatile organic compounds, PCBs, and total petroleum hydrocarbons) are found, additional sampling and inspections are conducted upstream to locate the source.

Business inspections

The City inspects and works with businesses to ensure that they are using best management practices to keep stormwater pollution, including hazardous materials and industrial waste, out of storm drains that flow to the LDW. We inspect businesses based on identified or potential pollution risk.

Pipe cleaning

When the City finds elevated contaminant levels in storm drain sediment, it 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.

Source control implementation

The City has a Source Control Implementation Plan (SCIP) that describes our work to control pollution sources over the next five years. Washington State Department of Ecology approved the City of Seattle's 2026-2031 SCIP in August 2025 to fulfill the requirements contained in Appendix 13 of the 20244 NPDES Municipal Stormwater Permit. More information can be found on Washington Department of Ecology’s website.

The Source Control Implementation Plan Documents are available for review:

Historical Content

The documents in the following section are described as “historical”. We provide this information as a resource for reference, research, or recordkeeping but no longer maintain it. This means that the information may have outdated contact information, non-functional links, or accessibility barriers for people with disabilities.

2021-2026 Source Control Implementation Plan Documents:

2015-2021 Source Control Implementation Plan Documents:

Fishing for safe seafood to eat

The only Duwamish River seafood safe to eat is salmon.

In the Duwamish River, the seafood that spend their entire lives in the river (perch, sole, flounder, crab, mussels, and clams) are unsafe to eat. They have high levels of toxic chemicals (such as PCBs) that you cannot see.

Learn how to protect your health while fishing for seafood that is safe to catch and eat: Eating Seafood—Public Health Seattle and King County: Fun to Catch, Toxic to Eat.

Seattle Public Utilities information