Project overview
Reconnecting waterways where roads act as barriers is a priority for the state. In western Washington, this means building hundreds of fish-passable structures under state highways to create habitat that is essential for meeting fish recovery goals.
A culvert below State Route 522 in Seattle is a barrier to fish migration through Thornton Creek, which drains into Lake Washington. As early as summer 2026, a Design-Builder working for WSDOT will begin installing new fish-passable structures that connect Thornton Creek under SR 522. This project will replace the culvert and rebuild the trim to reopen habitat and restore native fish population.
What to expect
WSDOT will select a qualified design-build contractor to complete the design of the fish passable structures for Thornton Creek. This project is fully funded and combined into a single contract with other fish passage projects on Interstate 5 and SR 524. Construction is currently anticipated to begin in mid to late 2026 and interstate closure needs will be determined by the type of structures and construction method proposed by the Design-Builder. Lane reductions on SR 522 are expected to be necessary during select periods of construction to build the culvert structure under SR 522.
While the timing of culvert construction largely depends on the Design-Builder, we anticipate construction could occur periodically over the span of 2 to 3 years. The exact dates and details of construction impacts will be announced closer to construction.
We will post important project updates as work progresses to our social media channels and weekly traffic news email once construction is underway.
By building a new fish passage under SR 522, we can return Thornton Creek to its natural stream conditions and open important spawning habitat to help several species recover.
