FREMONT — Larger than usual numbers of threatened steelhead trout swam from the ocean into Alameda Creek after heavy rains this year — and ran into the same concrete barriers that have blocked their migration for decades.

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On Wednesday, the fish got a lift in a decades long campaign to bring back the steelhead, an iconic seagoing trout, to the Bay Area’s largest creek.

Biologists and volunteers netted some of the 2-foot-long adult fish below a concrete barrier in the creek and trucked them two miles upstream for release in lower Niles Canyon.

The rescue teams also attached radio tracking devices to the fish to find out where they try to feed and breed.

In the end, five fish were netted and relocated. That yield might seem low for an ordinary fishing outing. Steelhead, however, are so rare that they are protected as a threatened species. The project to round them up Wednesday took more than 25 workers and volunteers from 10 organizations and the help of a local water agency in temporarily lowering water levels in the creek.

The rain-swelled creek didn’t lower as fast as expected, leaving the crews with about 30 minutes instead of two hours to capture steelhead before rising waters ended the project.

“It was a success to help five wild steelhead in a limited time window,” said Jeff Miller, executive director of the Alameda Creek Alliance. “I’m sure there are more there. We may come out next week and try it again.”

This was the first relocation of steelhead in Alameda Creek since 2008, and the largest in recent memory, organizers said.

Heavy rain and runoff this winter set up conditions for a big year of steelhead trying to move upstream in Bay Area creeks.

“These big pulses of water attract the steelhead and give them something to home in on,” said Joe Sullivan, the East Bay Regional Parks fisheries program manager. “The wet winter is good for the steelhead.”

The rescue team waited for more than two hours for water levels to drop low enough to allow workers to wade into the water and net the fish, which were blocked by a concrete weir built to protect piers supporting BART tracks on the Fremont line.

Plans are being made for a $10 million fish ladder to help steelhead and other migrating fish get past the weir, but that project is years off, Miller said.

After netting the steelhead, rescuers set up an assembly line on a pickup bed to weigh and measure the fish after soaking each one in the turgid, chocolate-colored creek water. A technician added Alka Seltzer to the water to calm the fish from the trauma of being handled through a wet towel.

Sullivan, the park fisheries manager, carefully wired the tracking device to each fish’s dorsal fin as passers-by walking dogs and riding bikes on a creekside trail stopped to check out the excitement.

BART trains zipped by as the biologists tended to the fish belonging to a species that was abundant a century ago before dams, water diversions and flood-control projects damaged or blocked access to spawning areas.

“You’ve got wild steelhead in this creek right next to BART tracks and a fairly industrialized area. What a contrast,” said Ted Shapas, a volunteer with the Diablo Valley Fly Fisherman, one of the groups helping with the project.

Organizers of the project said they believe the steelhead can return to spawn in habitat 20 miles or more inland in the Sunol and Ohlone regional wildernesses.

“There is a lot of good habitat far upstream,” Miller said, “if we can do projects to get them past these barriers.”