Rich Cowell brought his 3-year-old grandson to the Nimbus Hatchery on Saturday so he could see salmon jumping the fish ladder to complete their life cycle.

"They'll jump over each of those woods," the 52-year-old Penryn resident pointed out to Drew Chaddock.

Unfortunately the pair had to imagine the scene.

The fish ladder, which is a major regional attraction, is usually open for the annual American River Salmon Festival. But Saturday, during the festival's 12th run, the ladder was idle.

The closure was a precautionary measure because of concern over what's expected to be a small fall salmon run in the American River. The water's higher temperature could also lead to some salmon dying before they're able to spawn, said Bob Burks, manager of the hatchery.

"It's very stressful on the fish," he said.

The fish ladder, operated as part of the hatchery by the California Department of Fish and Game, accommodates salmon and steelhead returning from the Pacific Ocean and headed for spawning grounds farther up the river.

The festival, which ends its its annual weekend run today, usually draws more than 20,000 people to the hatchery and Lake Natoma in Rancho Cordova. Organizers didn't have a crowd estimate for this year's turnout.

The festival is coordinated by the Department of Fish and game, the U.S. Bureau of Reclamation, the U.S. Fish and Wildlife Service, the American River Natural History Association and the Save the American River Association.

Even though the only salmon some visitors may have seen Saturday were in a giant aquarium, Burks said the festival offers an opportunity for the public to learn more about the need to protect the river's natural resources.

"(It's) for folks to come out and have a great time, but to take away from it information about how fragile our resources are," he said.

There was no shortage of educational resources on Saturday. Groups such as the Sacramento Audubon Society and Friends of the River all had booths at the festival.

Except for a preview run during the festival, the fish ladder usually opens each year in early November. The peak of the fall salmon run is usually from mid-November to mid-December, Burks said.

The American River salmon run estimate for this year is just 6,000. Average numbers in the past year have been 35,000, with as many as 80,000 in some years, according to Mike Healey, an associate fisheries biologist for the Department of Fish and Game.

Burks said there is a combination of factors behind the decreased salmon population, including ocean currents and changing water conditions.

The low population numbers led federal and state officials to cancel most of the commercial and recreational salmon fishing seasons this year in Northern California.

It's lessons like the ones offered at the festival that can help future generations of migrating fish, officials said.

Another is a project, launched last week, aimed at deepening a side channel on the American River near Sunrise Boulevard Bridge in Fair Oaks. Salmon will benefit from the work, but the real winner will be the American River steelhead, considered threatened under the federal Endangered Species Act.

Steelhead use the channel for spawning when water flows are high, said Sarah Foley, deputy director of the Water Forum.

Lowering the channel will allow water and steelhead to move through it under lower flows.

At the festival on Saturday, Cowell said he'll come back to the hatchery later this year with his grandson.

"(You see) how hard the fish have to fight to have babies and start the new fish for the next round," he said.

"This generation can grow up to protect the natural resources," Cowell said.

Call The Bee's Sandy Louey, (916) 321-1088.