A seven-mile-long flood control channel on Mill Creek transitions to the natural channel west of Walla Walla. In 2008, a fishway was constructed to improve fish passage at this transition for ESA-listed summer steelhead and bull trout, and for reintroduced spring chinook. A flood in 2020 scoured the channel below the fishway, resulting in a five-foot jump for fish to enter the fishway. WDFW constructed a temporary repair using ecology blocks to build two weirs downstream to decrease the jump heights.

Tri-State Steelheaders sponsored an alternatives assessment which engaged stakeholders to select a preferred alternative that was developed to a conceptual level. In addition to about a dozen private landowners, the stakeholders include Confederated Tribes of the Umatilla Indian Reservation, Bonneville Power Administration, Washington Department of Fish and Wildlife, and the Mill Creek Work Group. The preferred alternative is a 1,200 foot long nature-like fishway consisting of a boulder-lined channel with pools and riffles. In addition, the banks will be laid back to reduce stream energy. Design work continued with a physical model study to inform design details. Final plans are expected in late 2024.