Duwamish River in-water contamination cleanup is about to resume

| Environment | South Park | West Seattle news

(King County photo, 2024 cleanup season)

The second of three seasons of in-water Duwamish River cleanup is about to begin. This is for the removal of contaminated sediment, in the works for decades, involving Boeing, the City of Seattle, and King County. Here’s the overview:

Construction in the upper reach, the southernmost two miles of the site, is scheduled to occur from October to February for three years, ending in February 2027. In-water construction activities are restricted to these months to protect certain fish species. LDWG completed in-water work for the first construction season from November 2024 – February 2025, with the second season beginning October 1, 2025.

Beginning October 1, the construction contractor will begin dredging contaminated sediment near the South Park Bridge and Duwamish River People’s Park.

Compared to the first construction season, cleanup activities this season will be more visible as the work moves closer to the South Park Bridge, homes, parks, and marinas. The community can expect multiple barges and equipment working on the water, lights for safe work during dark hours, and typical construction equipment noise.

Season 2 construction hours will be weekdays and Saturdays and will occur during both the daytime and nighttime. Work hours will vary based on factors, such as tides and the type of work being conducted (e.g., dredging or placing clean material). Work will be coordinated with Tribal fishing. During the first three weeks of October, in-water construction work is not currently planned for Mondays and Tuesdays when Tribal fishing is most active.

The dredged sediment goes by barge to a landfill on the Columbia River. More background on the contamination and cleanup are here. Cleanup-work updates will be on this website, including upcoming dates – not yet finalized (we’re told the ones currently listed online are likely to change) – for South Park Bridge closures.

P.S. For backstory, see our report from last year, before the first season of this work began.

Bill#1 September 24, 2025 (2:46 pm)

Does anyone have any insight of why this dredging works is – and has been – scheduled during spawning season?

22blades September 24, 2025 (3:12 pm)

Yeah, I was wondering the same thing.
- Chemine September 24, 2025 (3:59 pm)
  
  This window avoids juvenile outmigration. Spawning does not occur in the LDR and adult salmon transitting the area can avoid the dredging areas in ways that juveniles can’t.
- Eddie September 24, 2025 (4:48 pm)
  
  I think you can be pretty sure that the people responsible for planning and permitting this project have very expressly planned the project around the spawning seasons.

Dad September 24, 2025 (8:40 pm)

@ WSB or others. Does anyone know if the water is being monitored for contaminants during this process and if the data are publicly available? I think it’s great there is an effort to clean it up, just trying to understand if there is also an acute impact from the disturbance.

consultant September 24, 2025 (9:43 pm)

You can see the workplan and all EPA Superfund site documents on the Lower Duwamish Waterway Group website and through WA State Department of Ecology cleanup site.
North Admiral Cyclist September 25, 2025 (6:50 am)

Having worked in design and construction on the Seattle waterfront, I can say that all of Elliott Bay and the Duwamish have been studied and monitored for decades. Various efforts to clean up the contamination has been ongoing since at least the 1980s and before. Any “clean up” action will necessarily include monitoring after the clean up to verify it was effective.
K September 25, 2025 (11:02 am)

Yes, both conventional water quality monitoring for turbidity, temperature, and dissolved oxygen are being monitored frequently throughout the entire construction. There will also be chemistry sampling of the water for contaminants during certain dredging activities.

Sorry, comment time is over.