Project overview
Washington State Department of Transportation and contractor crews will replace existing fish barriers under I-5 and Old Highway 99 near Stanwood with three new fish-passable arch structures to restore fish passage.
On I-5 and Old Highway 99, crews will replace existing culverts with three new 68-foot-wide steel arch culverts, ranging from 50 feet to 70 feet long. Crews will rehabilitate the approximately 2,000 feet of creek channel from the west side of Old Highway 99, through the I-5 median, and to the east side of Northbound I-5.
The new crossings will provide stream habitat gain of 8,215m (nearly five miles) which support the populations of salmon, steelhead, other aquatic species, and wildlife.
What to expect
Construction is scheduled for February 2025 to December 2026.
Northbound I-5 and Southbound I-5
Construction of both Northbound I-5 and Southbound I-5 will begin early 2025. Lane reductions will begin in February and will last eleven months. During this time, drivers will be shifted onto a temporary two-lane bypass roadway for nine months while excavation and arch culvert installation occur. Northbound and Southbound I-5 construction is anticipated to be complete in early 2026.
Old 99
Old Highway 99 is anticipated to be closed for six months in 2026 to construct the final fish-passable structure. During this time, freight and local traffic will be detoured to I-5. Local traffic may also choose to use 4th Avenue NW.
