Biologists with special water-filled, aerated backpacks trudged up a remote creek in Northwest Sonoma County on Tuesday, carrying their precious cargo of hatchery-raised coho salmon to release into the wild.

Within a couple hours, they had put 4,000 juvenile fish into Devil Creek, part of an ongoing program to re-populate the Russian River with the endangered coho.

"They're really beautiful," Ken Leister, an Army Corps of Engineers animal care specialist, said as he used a small net to scoop up and examine batches of writhing fingerlings.

"You get the gold and the green color and some blues," he said, pointing out the subtle hues of the fish before they were placed strategically along a half-mile of the creek.

The coho salmon re-stocking program began a decade ago when scientists took some of the last remaining wild juvenile coho from Russian River tributaries and raised them in special tanks at the hatchery at Warm Springs Dam.

The captured fish were spawned, and their offspring tagged and released into a dozen creeks in northern Sonoma County that flow to the Russian River.

Coho mature in fresh water and go to sea before returning to spawn and die, all in about a three-year life cycle.

In a promising sign of their recovery, the fish have been coming back to the tributaries to reproduce and hatch in the wild.

"It was definitely a good thing to document," said Jeff Jahn, a biologist with the National Marine Fisheries Service. "Last year an estimated 200 Coho returned to the Russian River — a record return in over a decade."

Scientists counted 89 juvenile coho this winter that spawned naturally in Devil Creek, which flows into East Austin Creek and the Russian River.

"They're very healthy, very happy fish," said Ben White, a biologist with the Pacific States Marine Fisheries Commission.

The biologists are among the federal, state and county officials overseeing the coho restoration on the North and Central California coast.

On Tuesday, they were part of the caravan of fish and scientists who made their way over four-wheel drive roads, criss-crossing streams to the 440-acre property designated as the East Austin Creek Conservation Bank.

In addition, they brought dead adult salmon to place into the creek to serve as nutrients for the juvenile fish and other critters. Doing so mimics the die-offs of fish that used to occur naturally when the population was thriving.

Owned by Nancy Summers and her husband Peter Gruchawka of Kenwood, the rugged land with a deep shaded canyon is considered ideal for the coho as well as steelhead population.

The couple said they initially set out to restore the habitat but last year it became the nation's first conservation bank for coho. That means they can sell conservation credits to developers and government agencies whose projects impact salmon habitat.

The logging last century on the property had a devastating effect on the fish.

"The easiest way to log was to drag the trees down the creek. It denuded the area. There was no tree cover and the water was too warm," Gruchawka said as he stood in the shade of the revitalized tree canopy.

With the help of the California Conservation Corps, the couple augmented the natural growth by planting hundreds of trees and placed large remnants of redwoods and woody debris in the creek to create fish shelter.

Gruchawka said there hadn't been any coho seen in the stream in more than a half-century.

But last year, fish were spotted reproducing. They included a male wild salmon and a female with a clipped fin, indicating a hatchery fish.

"To have fish breed in the first year is pretty phenomenal. We weren't expecting that quick a result," said Peter LaCivita, an Army Corps fishery biologist.

If successful longterm, the effort eventually could help commercial and sport-fishing.

"We're trying to get enough wild population out here so we don't have to stock the fish," said LaCivita.

"It would be nice to recover the fish so you could rod and reel them on the Russian River. You can't do that now," he said.