The American River once hosted thousands of steelhead migrating upstream from the ocean in three separate runs. Today it's down to just two runs of a few hundred fish.

The Sacramento was the only river in western North America with four salmon runs. They numbered in the millions – so numerous that American Indians and settlers could catch a salmon dinner with their bare hands. Now one run is gone, and two are endangered. The fourth could join them soon.

Restoring a fragment of that spectacle to the Central Valley is the goal of rules proposed by the National Marine Fisheries Service. The service wants, among other things, restoration of winter- and spring-run salmon above Shasta Dam on the Sacramento River, and steelhead above Folsom Dam on the American River.

Combined, the fish transit order is considered the biggest of its kind in U.S. history.

Making it happen presents huge financial and engineering challenges. Costs could exceed $1 billion at a minimum – more than 10 times the original construction cost of both dams.

"It's pretty substantial, the amount of work that's required," said Mike Chotkowski, regional environmental officer at the U.S. Bureau of Reclamation, which operates the dams. "We still haven't even determined whether it's feasible."

The fisheries service says that without restoring access upstream, it's likely the three fish species will go extinct. Climate change means it will be harder to maintain cold-water habitat below the dams, so they must have access to better habitat.

"The fish are at that jeopardy point where it's important for us to take immediate steps," said Howard Brown, Sacramento River basin chief for the fisheries service.

The rules proposed this month, called a biological opinion, were developed in response to a lawsuit brought by environmental groups. Federal Judge Oliver Wanger agreed with their claim that prior rules, which had no fish passage requirement, did not prevent extinction.

The ruling raised anxiety among California water managers. Thirty agencies sued last week, alleging that the fisheries service didn't follow procedure in adopting the rules.

Other experts argue there are cheaper ways to rescue the salmon populations.

Among them is the volunteer group Save Auburn Ravine Salmon and Steelhead. It has worked quietly over the past year to remove small obstructions on Auburn Ravine, a little-known tributary of the Sacramento River.

The natural ravine flows with spring water and sewage treatment outflows starting in Auburn.

Accounts as recent as the 1960s show that the ravine once hosted robust fish runs, said John Rabe, a member of the group's board.

Four adult salmon were observed in the ravine last winter. The group expects hundreds next winter and plans a salmon festival in Lincoln to welcome them back.

Rabe said 600 small creeks between Modesto and Redding also could be restored – at far less cost than fixing the big dams.

"Don't waste time and money on the dams. Spend it on the creeks," he said. "That would open literally thousands of miles of spawning, which would make a huge, huge difference."

The federal rules don't specify how salmon and steelhead should be moved around the dams. Instead they require studies, starting in December, to find the best solution that can be in place by 2020.

By March 2012, water agencies must begin moving fish around the dams on a trial basis. This will probably be done by loading fish into trucks.

Experts say moving fish around Folsom and Shasta dams is a job as big as the dams themselves. Shasta, completed in 1945, stands 602 feet high. Folsom was finished in 1956 and soars to 340 feet tall.

They were built without any means to pass fish upstream, and each has a smaller dam downstream to regulate flows: Nimbus on the American, Keswick on the Sacramento.

Distance and elevation required to move fish upstream may eliminate the option of a traditional fish ladder at both dams, said Alex Haro, a research ecologist at the U.S. Geological Survey fish laboratory in Turners Falls, Mass.

Call The Bee's Matt Weiser, (916) 321-1264.