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West Duwamish Wet Weather Storage

King County will build a wet weather storage facility to hold stormwater and wastewater during large storms, reducing overflows into the Duwamish River.

Project description

Aerial map displaying location of the new storage facility and associated structures (two underground structures and two outfall/overflows) next to the Duwamish River.

King County will build a 1.25-million-gallon underground storage tank near the intersection of Southwest Michigan Street and Second Avenue Southwest to hold stormwater and wastewater that currently overflows into the Duwamish River during large storms. The water in the storage tank will then flow to the West Point Treatment Plant for treatment before it is safely released into Puget Sound. This storage tank will reduce overflows and pollution into the Duwamish River. The County will also build supporting infrastructure underneath West Marginal Way Southwest.

Project design is now complete. Construction is anticipated to begin as soon as early 2026.

Project update

Summer 2025

Construction is coming soon! 

Now that the design phase of this project is complete, King County is preparing for construction. We expect construction to start as soon as early 2026 and continue through 2028.

Find us at upcoming events near you!

Meet us at one of these upcoming events to learn what to expect as we get closer to construction.

  • Wellness Tuesday: Cultivate South Park and Seattle Parks and Recreation are partnering to host Wellness Tuesday events in the South Park neighborhood this summer. These events include a farmers market pop up, information tables, games, and other family-friendly activities. Find us at this event on Tuesday, July 15, from 4:30 pm to 7:30 pm at South Park Plaza, 8456 Dallas Ave. S.
  • South Park Summer Party (SOPASUPA): Cultivate South Park and the South Park Business District will celebrate community at the annual SOPASUPA event. The event will include vendors, information booths, and activities. Join us Saturday, August 16, from noon to 8 pm in the South Park Business District.

Explore our new project resources

Use the links below to learn more about the West Duwamish Wet Weather Storage project and responses to the questions we frequently hear from you!

Sign up for project updates

Stay in the loop as we prepare for construction! Subscribe for project updates by email or text to get updates, surveys, notices, and other information by email and/or text. You can unsubscribe anytime.

Previous project updates

Consultants, contractors & suppliers: learn about upcoming contract opportunities including the West Duwamish Wet Weather Storage Facility.

Project location

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