The steelhead trout and Chinook salmon of the American River have the Bureau of Reclamation to thank for restoring more than 15,000 tons of gravel to increase spawning habitats.

A popular spawning site along a two-mile stretch of river below the Nimbus Dam had become too shallow to allow the fish to properly reproduce.

“Space was limited. Eggs were laid on top of other eggs. Survival was not what it could be,” said Bureau of Reclamation Fisheries Biologist John Hannon.

With the Nimbus Dam blocking downstream flow, Hannon said the good spawning gravel was being carried away by the current without being replenished. Gold mining in the 1800s had left many of the river’s side channels dried or blocked-off, keeping the fish from the vegetated areas that serve as prominent juvenile rearing habitats.

Using GPS markers and aerial photographs, the Bureau of Reclamation monitored the “redd spots” where the fish species tend to build nests.

“Populations have declined greatly since a record high in 2002,” Hannon said in an e-mail. Regarding the amount of redds (nests) of each species in the generally-popular spawning area near the Nimbus Dam, Hannon said the redd count had fallen to “less than 1%” of its highest peak.

In 2008, the Bureau of Reclamation began its five-year plan to restore the fish population, working in partnership with the Water Forum, U.S. Fish and Wildlife Service, California Department of Fish and Game and Sacramento County Regional Parks.

The Water Forum is a collection of agricultural leaders, citizens and environmentalists who monitor and protect Sacramento’s rivers. Hannon said it was crucial to gain their support before moving forward.

“Everyone has been very supportive,” Hannon said. “It took about a year to get the project ready for proposal.”

Split into five phases, the plan involved adding gravel to specific areas of the American River to increase opportunity for the fish to spawn, as well as improve the overall ecosystem for aquatic insects and birds.

The first and second phases focused mainly on areas near the Nimbus Hatchery. The first phase brought in spawning gravel to improve the redd count and larger gravel to help produce invertebrates, the bugs that fish eat.

“The first year results regarding spawning at this site consisted of 81 Chinook redds and 68 steelhead redds,” Hannon said in an e-mail. He said the area now hosts 14% and 74% of the river’s salmon and trout nests, respectively.

Phase two focused on rebuilding juvenile rearing habitats downstream in the American River side-channels. The plan succeeded in garnering up to 31% of the river’s salmon nests between 2008 and 2009.

Phase three was completed on Sept. 27.

“We modified the topography of the river,” Hannon said. “In some areas, the water rose as high as a foot, and widened almost 20 feet onto the shore.”

Workers from the city of Sacramento ran processing equipment that cleaned and created different sizes of gravel. The larger gravel filled in the down-cut areas to return water to side channels and grant the fish access to vegetation. The smaller gravel is where the fish prefer to make nests for their eggs.

“We got pretty much everything done,” Hannon said. “I’d say we put in about 90 percent of the spawning gravel we wanted.”

Hannon said crews could end up working on the same two-mile stretch of river beneath the Nimbus Dam, depending on whether the alterations hold up to nature. If they perform well, the project will continue to Phase 4, which involves distributing more gravel and restoring other sites along the river.

“We have three more sites to work on. One by the Nimbus Dam, one near Sailor Bar and another at River Bend Park,” Hannon said.

The work at Nimbus Dam will coincide with the start of renovations planned for the Nimbus Fish Hatchery, which may not happen for another two years. Hannon said they may begin work at River Bend Park later this year.

“Currently the majority of the returning adult fish are from fish hatched and released from Nimbus Hatchery,” Hannon said in an e-mail. “The ultimate goal is to double the population of naturally produced Chinook salmon and steelhead trout.”

For more information about the American River gravel restoration project, click here.

Photos from John Hannon and the Bureau of Reclamation.