WALLA WALLA, Wash. -- Contractors recently completed construction of the upstream northeast and northwest retaining walls at the Mill Creek Fish Ladder Project. These walls will connect to the upstream gate wall and fish ladder exit, expected to be completed by October. The retaining walls will allow the project to enter its next phase without reinstalling a cofferdam during the upcoming high-water season.
Together these structures will provide protection during high flows. As a result, the cofferdam -a temporary enclosure used to pump water out of the work area - will not be needed during the next flood season. The cofferdam was removed in June 2026 when in-water work began.
The existing fish ladder at the Diversion Dam, built in 1982, no longer meets National Marine Fisheries Service standards for successful fish passage, which causes steelhead, Chinook salmon and bull trout to face challenges returning to spawn in Mill Creek.
The new fish ladder will feature improved waterflow to attract and a better passage design, significantly reducing the time fish spend navigating the Diversion Dam and improving access to critical spawning habitat in upper Mill Creek. The project includes improvements to the dam’s downstream pool, a bypass channel for juvenile fish traveling downstream, and bypass gates that allow sediment to be flushed past the dam.
Upon completion, the new fish ladder will improve fish passage while enhancing U.S. Army Corps of Engineers’ ability to manage flows during flood events, supporting both ecosystem restoration and flood risk reduction for the Walla Walla Valley. This project represents a significant investment in both community safety and environmental stewardship.
Construction is expected to continue through fall 2027.
For more information about the Walla Walla District and to learn about the Mill Creek Project, visit: https://www.nww.usace.army.mil/Locations/District-Locks-and-Dams/Mill-Creek-Dam-and-Bennington-Lake/
Release no. 26-025