I-5 impacted by Fish Culvert Replacement near Arlington

SNOHOMISH COUNTY, MARCH 10: It’s only March, but the road construction season is already getting underway in the North Sound. A big project to keep an eye on is along I-5 just south of the Stanwood interchange.

This project is part of the court-ordered restoration of the fish passages, replacing fish-blocking culverts across the state. Culverts are a structure that allows water to flow beneath and obstacle, such as a road of embankment. 

This project will replace existing fish barrier culvert crossings under I-5 and Old Highway 99 with three new fish-passable structures.

What’s Happening

Overnight closures of one lane in both directions of the freeway have already started. The work involves building temporary two-lane by-pass roadways for both directions of I-5 to the west of the current freeway. It is expected to last through April.

Washington State Dept. of Transportation (WSDOT) spokesperson Madison Sehlke said, “There will be two-lane by-pass roads in each direction, so one north and one south. They are standard lanes, 12 feet with standard shoulders as well. Once traffic is on the by-pass road, there will be a speed reduction to 60 miles per hour.”

Once the by-pass roadways are in use, WSDOT crews can then remove the current box culverts. Crews are expected to dig down about 80 feet to restore the natural creek bed.

The replacements will be two arch culverts in each direction, not only restoring the creek to its natural setting but also providing a wildlife connectivity corridor benefiting local wildlife such as deer and beavers. Each arch culvert will be about 68 feet long.

“We’re expecting that the by-pass will take eight weeks to complete so that does put us at the end of April or beginning of May, just in time for our Skagit Valley Tulip Festival,” Sehlke said.

Traffic Delays

With the freeway by-pass involving only two lanes in both directions and a speed limit of 60 mph, expect delays through this construction zone not only during the Tulip Festival but any travel for the rest of the year.

“This is a two-year project. We’re hoping to have traffic shifted back [on the main line] by the end of December,” Sehlke said.

Once traffic returns to the interstate’s main line, crews will then close Old Highway 99 for six months, beginning in early 2026 as more culvert replacement work continues.

WSDOT is encouraging people to avoid peak times if possible when traveling through the area, but if they are traveling through those peak times expect delays and factor in extra travel time.

The cost of this culvert replacement project is contracted to cost $57.5 million and is funded by the Move Ahead Washington Transportation Funding package.