Washington State Department of Transportation – SR 203-Loutsis Creek Fish Passage

During the summer of 2020, contractor crews working for the Washington State Department of Transportation built an arched structure – the first of its kind on the West Coast – allowing Loutsis Creek to flow freely underneath SR 203 just south of Duvall. Before this project, the creek went through a five-foot diameter concrete pipe buried about 40 feet under the highway. Water traveled too swiftly through the pipe for salmon and other fish to continue upstream. The new creek bed opens up access to about 3.1 miles of additional habitat and spawning grounds for Coho salmon, steelhead, coastal cutthroat trout, and resident fish such as trout and lamprey. The new structure incorporates one-foot diameter arched fiberglass tubes to form its frame, with the tubes filled with concrete and covered with composite plates. Crews then returned fill material and repaved the highway. This pilot project demonstrated the effectiveness of this type of construction, which reduced the time and expense compared to other construction methods.