The state Department of Transportation in the spring will build a new dike near Dugualla Bay on north Whidbey, rerouting traffic from Dike Road for about three months, the department said this week.

The project has been under discussion since early this year.

Plans call for crews to start clearing invasive plants along Dike Road next week.

Then, in the spring, crews will build a new dike just east of the southern half of what is currently Dike Road. That will restore as a wetland the area to the east of the new dike, the department said.

Dike Road will be rebuilt atop the new dike.

Dugualla Bay supported a saltwater marsh until 1918, when local residents built a dike along what is now the beach, in order to create farmland, the department said. Dike Road was built a little later.

The DOT will also breach the old dike in two places, allowing Dugualla Bay to flow into the wetlands as the tide rises. These actions “will restore about 23 acres to their natural state and provide habitat for juvenile salmon,” the department said.

“The Dugualla Bay site has been recognized by numerous state agencies as one of the top salmon restoration priorities in the state,” Ryan Elting, conservation director for the Whidbey Camano Land Trust, said earlier this year.

Previous improvements to the area have “greatly limited” salmon’s ability to use the area, Elting said then, and the Dike Road project will be “restoring the estuary habitat” in Dugualla Bay.

The new dike will stand 15-20 feet tall and will be built to U.S. Army Corps of Engineers’ post-Hurricane Katrina standards, the department said.

The project’s total cost will be $4.5 million.

The project is part of the State Highway 532 Davis Slough bridge project. To expand that road, the department placed fill over about 3.6 acres of wetlands. State and federal law requires new habitat to compensate for the loss.

The Dugualla Bay property is located about 12 miles northwest of Davis Slough.