Project overview
As part of WSDOT’s fish passage program, we will remove two culverts that do not allow fish to pass and replace them with fish-passable structures along Unnamed Tributary to Big Soos Creek and Unnamed Tributary to Soosette Creek at State Route 18 in Auburn. The new structures have the potential to open nearly one mile of habitat for coho, steelhead, sea-run cutthroat and resident trout.
What to expect
Work on both SR 18 sites is scheduled to begin fall 2026 and end winter 2029. Both culverts cross SR 18 where two lanes travel west and three lanes travel east. Crews will work in one direction and one lane of the highway at a time. Travelers can expect single-lane closures. Lane closure dates have not been set.
WSDOT will remove two culverts that do not allow fish to pass and build two fish-passable structures under SR 18 in Auburn.
Two unnamed tributaries cross under SR 18 through steel culverts, one flowing to Big Soos Creek and the other to Soosette Creek. Both culverts are not passable for fish because they are too high, creating a drop-off too high for fish to successfully jump up and preventing fish from traveling upstream. The steel culvert along Big Soos Creek is beginning to decay.
When replacing fish barriers, we must build structures and improve the stream so that fish can use it year-round at all stages of their life. That means during summer months when streams are usually lower, the stream must be usable by juveniles and adults. During winter, when water tends to run higher and faster, the stream must also have areas where fish can rest.
New fish passable structures
To replace the two existing culverts, WSDOT will build two new fish-passable structures. We'll also add woody vegetation, logs and other wood to this section of the unnamed tributaries to provide channel complexity and diversity, such as pools that provide refuge for young fish. These habitat elements enhance rearing and spawning habitat for fish. The improvements mean fish will have access to nearly one mile of habitat that was previously inaccessible.
This work is part of our fish passage program. Replacing the existing culverts and rebuilding the stream channels expands healthy fish habitat; an important step in restoring fish runs and increasing populations. This benefits commercial seafood operations and recreational fishers and provides more food for a declining orca population. Additionally, replacing these fish barriers helps us meet our obligation to remove barriers under the 2013 U.S. District Court injunction.
