The coho salmon fingerlings released into Dry Creek with much fanfare Friday moved toward cover in a flash among the rocks and tangled branches placed specifically to provide needed shelter.

The slender, silvery fish, each just 3 1/2 to 4 inches long, flipped from their nets carrying the hopes of their human stewards, their future survival perhaps determining the fate of their species after decades of depletion.

The wriggling juveniles, about 2,000 of them, are pioneers in a grand experiment undertaken by the Sonoma County Water Agency and the Army Corps of Engineers to enhance the Dry Creek habitat in ways specifically designed for the needs of the young endangered coho at the developmental stage of those released.

Improvements include several side and back channels excavated from areas off the main creek channel, creating large areas of sluggish flow where young coho can rest, feed and grow before venturing beyond Dry Creek toward their eventual migration into the Pacific Ocean in spring and summer.

More than mere ditches dug into the ground, these channels represent the latest in engineering and design, featuring river gravel and rock beds, log jams, huge redwood stumps and boulder fields intended to disperse the energy and speed of the current and offer cover to the fish.

Fallen leaves, duck weed, even algae already have accumulated among the hand-placed logs and root wads in some areas, turning the man-made channels into natural looking areas that are hard to pick out from what nature made.

Willow stumps newly planted densely along the edge should in short order provide shade for the summer months that will further enhance the prospects for the juvenile coho living there, officials said.

Though steelhead trout and Chinook salmon, both federally listed as "threatened," also will benefit from the work, the effort is primarily geared toward the exclusive rearing needs of the juvenile coho for areas of slow-moving and still water.

The overall aim is to enhance coho habitat along a cumulative six miles of the 13.9-mile stretch between Warm Springs Dam/Lake Sonoma and its confluence with the Russian River near Healdsburg.

The fish will be monitored closely to see how their new digs suit them in the coming months, before they head downstream toward the ocean, even as plans proceed for a second phase of habitat enhancement slated to be done next year.

Releasing the fish "is better than cutting a ribbon" to mark the first phase completion, said Army Corps. Lt. John Baker, commander of the San Francisco District which includes Warm Springs Dam and a stretch of creekbed just below it where some of the habitat restoration work was done.

"Hopefully, in two or three years we're going to be back here and watch them return" to spawn, water agency General Manager Grant Davis said.

The creek improvements celebrated Friday came at a combined cost of about $11 million. They represent the first part of a 12-year project developed under orders from the federal National Marine Fisheries Service to offset degradation of the stream habitat stemming from the operation of Warm Springs Dam.

Over the three decades since the dam was built across Dry Creek, creating Lake Sonoma and providing both a water source for some 600,000 consumers and flood-control protection, portions of the creek have been narrowed into channels that funnel the water at high velocity.

Water releases for urban and agricultural users in the summer, and winter-time releases to ensure sufficient flood-control capacity for incoming rains, have added to the adverse conditions for the coho, especially those over-wintering in Dry Creek as juveniles. Erosion has additionally damaged the habitat, officials and biologists said.

But there is an ironic twist: the existence of the dam took a creek aptly named for is historically dry summer conditions and provided it a plentiful, year-round source of cold water that is ideal for salmon and steelhead.

That cold water would not be available during the critical summer months if not for the dam, producing an opportunity to create a habitat where the coho can truly thrive, said Dave Manning, environmental resources coordinator for the water agency.

"The abundance of cold water in Dry Creek is the driving force behind this restoration," he said.

The NMFS biological opinion, issued in 2008, included a timetable that gave urgency to scientific studies to determine where the greatest opportunities for habitat enhancement existed.

Most require cooperation from private property owners, including many wineries. A collection of landowners near Lambert Bridge were among those most willing to participate, narrowing down the options for the first phase of water agency work, Manning said.

Initially taken aback by unexpected construction on ancestral tribal grounds just below the dam, the Dry Creek Band of Pomo Indians also came onboard, and negotiated a lease with the Army Corps to use the 27-acre area for cultural celebrations and other uses. Tribal elders participated in releasing the fish Friday.

The 2,000, 9-month-old advanced fingerlings were among about 100,000 born at the Don Clausen Hatchery to be distributed over several weeks to tributaries within the watershed as part of the usual fall release, Manning said.

"It's really gratifying to study the fish in the watershed for all these years and now to be able to put together a project like this," he said. "It's a win-win for all the parties involved."

(You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.)