BELLINGHAM - Crews will build a bridge on Old Fairhaven Parkway this summer, in anticipation of work to improve salmon habitat at Padden Creek.

Next year, Padden Creek will be restored to its original channel and routed away from a 120-year-old tunnel that is virtually impassable to migrating fish. The creek will flow under the new bridge, near 20th Street, where construction is scheduled to begin on May 1.

Instead of a detour, there will be a short, paved bypass road next to the bridge construction site. Traffic flow should be nearly normal through the bypass, Department of Transportation spokesman Dave Chesson said.

"Even though it's in an area that has a lot of traffic, it should be easy," he said.

Crews will avoid working weekends, when summer activities are usually scheduled in Fairhaven, Chesson said. The project site is close to homes, so DOT has not yet sought permits to work at night, project engineer Chris Damitio said in an email to city engineers.

Access to 20th Street north of Old Fairhaven will be closed during construction, Damitio said. Pedestrians and bicyclists will be able to get through the project area.

Construction should wrap up around Thanksgiving, Chesson said. Some minor finishing work may be required in spring 2014.

DOT will begin soliciting bids from contractors on Monday, Feb. 25, Damitio said. The project's estimated cost, including preliminary design and engineering, is $2.6 million.

Only a rudimentary design has been completed for next year's work to improve Padden Creek, but it is expected to cost more than the DOT's bridge, said Rory Routhe, Bellingham's assistant director of engineering. Most of the funding for the project is already available, with some coming from a Department of Ecology grant.

The creek is home to chum and coho salmon primarily, in addition to chinook salmon, and steelhead and cutthroat trout. In good years, the creek is teeming with fish.

In 2004, "you couldn't go across Padden Creek without stepping on fish," Happy Valley Neighborhood resident Richard Sullivan said.

The 2.7-mile creek from Lake Padden to Bellingham Bay is so crowded in part because fish are restricted to its lowest reaches, downstream of the 2,200-foot-long brick tunnel built in 1892.

"They can return in larger numbers than that area can support, and the fish spawn on top of each other," said Rachel Vasak, executive director of the Nooksack Salmon Enhancement Association. The group has organized relocations of spawning salmon in Padden Creek to points upstream of the tunnel.

The improvements to Padden Creek have been on the drawing board for a decade or more. In anticipation of the project, NSEA restored salmon habitat above the tunnel years ago, even though few if any salmon were making it that far upstream.

The creek improvement also will reduce flood risk, city officials said. Sullivan said there have been two big floods in Happy Valley since his arrival in 1978.

Reach Ralph Schwartz at 360-715-2289 or ralph.schwartz@bellinghamherald.com. Read his politics blog at blogs.bellinghamherald.com/politics or follow him on Twitter at @bhamheraldpolitics.