The first of about 3 million young salmon were released into the American River Thursday, and California Department of Fish and Game officials said they will finish the job Friday. They hope those fish will return to spawn within two to five years.

“They were spawned, hatched and partially raised at the Nimbus Fish Hatchery in Rancho Cordova,” said Dana Michaels, information officer for the Department of Fish and Game.

About 25 percent of them have coded wire tags in their noses so Fish and Game staff will be able to track how many of them are returning to their native grounds to spawn.

The goal, Michaels said, is to return the number of fish to their natural levels – levels that have dropped severely since the Gold Rush.

“There used to be millions and millions of salmon before we developed and affected their habitat,” she said. “Our real goal is to improve the return rate. We’d love to get it back to historic numbers.”

Releasing the fish under the Jibboom Street bridge in the River District has previously been successful and shown the strongest rates of return, but fish are also released in other areas, she added. One of the other areas is the San Francisco Bay, and there are other river locations as well.

The biggest effects Californians have had on the fish population stem from the building of dams – which blocked their waterways – and mining, which increased silt levels in the rivers and caused them to become shallower.

Releasing fish into the river is not a new program for the area, said Laura Drath, fish and wildlife interpreter at the Nimbus Fish Hatchery.

“The hatchery was built in 1955, at the same time as the Folsom and Nimbus dams,” she said. “Our mandate is to produce 4 million salmon and 430,000 steelhead trout every year.”

The hatchery was built by the federal Bureau of Reclamation as a result of about 100 miles of spawning ground being eliminated by the dams’ construction.

According to Drath, there is now only seven miles of habitat the fish can use to spawn because the dams blocked off the rest of the river.

Some hatcheries, she said, aim to increase the fish population, but the Nimbus hatchery is mandated to only replace what was lost from the historic numbers.

Michaels said monitoring the salmon population is integral to ensuring it isn’t over-fished.

“The last couple of years, the salmon population has collapsed,” she said. “We had to cancel two commercial fishing seasons.”

Water levels play into that, and the last three drought years were bad for the fish, but this year has produced good amounts of water, she added.

The fish released into the water this week should not be seen as a meal ticket to anglers, as Michaels said it is illegal to catch or possess them.

The salmon are only about 3 inches long, and anything less than an adult – usually about 12 inches – is illegal to catch on the American River.

Regulations vary by river, and the Department of Fish and Game has a complete list of regulations here.

The Nimbus Fish Hatchery, located at 2001 Nimbus Road in Gold River, has a free visitors center open from 10 a.m. - 3 p.m. every day except Christmas. Outdoor areas at the hatchery are open from 7:30 a.m. - 3 p.m. every day except Christmas.

Brandon Darnell is a staff reporter for The Sacramento Press. Follow him on Twitter @Brandon_Darnell.