SR 203 - Loutsis Creek - Fish Passage - Complete September 2020


During summer 2020 our contractor crews 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 5-foot diameter concrete pipe that was 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 like trout and lamprey.

The new structure incorporates 1-foot diameter arched fiberglass tubes to form its frame. The tubes were 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 that other construction methods would have required. It is being added to our list of approved methods.

How you benefit

Environmental: Replacing the culvert restores Loutsis Creek to a more natural state and improves passage for resident and migratory fish and aquatic life.

Economic: This pilot project demonstrated this type of construction can be effective for certain culverts, reducing the time a highway needs to be closed and reducing construction costs.


The total estimated project cost is $8.2 million, using state and federal funding.


Northwest Region Communications
15700 Dayton Avenue North
Seattle, WA 98133


A small map showing the location of Loutsis Creek near Duvall.