Forty-feet of 7-foot-diameter culvert piping will soon welcome salmon to the upper reaches of Cooper Creek.

A fish enhancement project under way at the head of Eagle Harbor removes a concrete structure blocking the creek, allowing adult and juvenile coho salmon and searun cutthroat trout to reach another half-mile upstream for spawning and nurturing young fish.

The new habitat should help boost the fish population.

“We have a pristine area of watershed fed by a spring providing a valuable source of clean, cold water for fish use,” said Wayne Daley, a fisheries biologist who has worked with the city. “It’s one of the best wetlands on the island, in terms of having a stream originate in a wetland.”

The project is a part of a priority system established by city’s Department of Public Works and the Bainbridge Island Watershed Council to improve fish passage on local creeks. Work on Manzanita Creek is planned for next year.

“A critical fact that contributes to the decrease in the number of salmon is loss of ‘rearing habitats,’ where juveniles grow up,” Daley said. “Coho need 18 months of freshwater environment before going to sea.”

Coho salmon and searun trout, which go into and out of salt water every three to six months, were previously able to swim into Cooper Creek, but could not get to city-owned land beyond barriers except during high water events.

In a smaller habitat, Daley says only a limited number of juveniles can be reared since they must compete for space. Fish need both a pool habitat for rearing young and a spawning habitat with a proper gravel bottom and flow characteristics.

With an extra half mile of stream, Daley estimates, “it would not be unusual to support an additional 30-40 adults (fish).”

The $66,974 project removes an obsolete concrete impound – last used by the city in the early 1970s to divert creek flow to the city water supply – with a 40-foot culvert, to take the creek below a gravel road.

The project has been in the works for almost eight years, said Melva Hill, the city’s project manager. The project was unexpectedly difficult, the most challenging Hill said she has encountered.

The crew from Lydel Construction has battled groundwater seeping into every hole they dig. Heavy rains last Friday nearly washed out the entire day, as creek waters rose 9 inches in three hours; the city’s operations crew came to the rescue with extra pumps. It took six pumps to keep up with the rising waters.

Also, since the reservoir tank is fed by three wells on the other side of the creek, crews had to set up water crossings to keep well water supplying the reservoir.

An additional task of replacing old water pipes required a one-day shutdown of water to homes from Finch and Sportsman Club Road to Wyatt Way.

The culvert bottom will be layered with a gravel bed to mimic the natural habitat as closely as possible.

The end of the creek exiting the culvert has already been shaped into a “riffle pool” system – gravel-bottomed pools with gravel bars resembling gentle stairs between each pool. Cold water, like from a good drinking fountain, flows from pool to pool.

Based on the city’s studies, “this is the coldest creek on Bainbridge Island,” Hill said. “It makes for excellent (salmon) habitat.”

Hill says she enjoys working on fish enhancement projects. Last year she worked on the Issei Creek Fish Enhancement Project.

“Normally we don’t experience fish runs the first year, but we had fish runs the first year (at Issei Creek),” Hill said. “I was really surprised because I was told it takes several years for fish to return.”

The project will wind up next week. Then the city will watch for the creek to “silt” – that is, for sediment to settle into the new, porous creek bottom and seal it, keeping creek water from soaking into the ground. Silting is a prerequisite for fish returning.

Other major island streams which support fish include Spring Ridge Brook, Issei Creek, Manitou Creek and the Schel-Cheb Creek and Estuary.

“I hope for immediate use (of Cooper Creek by fish) as we have experienced in other streams on the island,” Daley said. “In five to 10 years, I expect to see a significant increase in streams, but also in fisheries for sport, commercial and tribal fishing.”