These Chinook almost went extinct during California’s drought. Can this $100 million plan save them?

During the worst of California’s five-year drought, thousands of eggs and newly spawned salmon baked to death along a short stretch of the Sacramento River below Shasta Dam.

The winter-run Chinook, already hanging by a thread, nearly went extinct.

Hoping to avoid a repeat of that dire scenario, fisheries officials announced Thursday the launch of a plan — nearly 20 years and $100 million in the making — they say would expand the spawning range of the fish to include a cold-water stream called Battle Creek. The idea is that the stream could keep the fragile winter-run alive as California’s rivers get hotter because of a warming climate.

The stakes are high and go well beyond the fate of the fish. Concerns about this run of salmon have a major impact on how water is distributed to farms and cities across California.

During the drought, for example, farmers experienced cuts to their water supply as dam managers held water in Shasta, the state’s largest reservoir, in a frantic effort to ward off extinction of the Chinook.

On Thursday, fisheries managers said that over the coming weeks they were going to release around 200,000 young winter-run Chinook raised at a hatchery to Battle Creek, which feeds into the Sacramento River below the dam near Anderson in Shasta County.

Thanks to cold springs that keep the stream flowing all summer long, Battle Creek long has been considered a possible sanctuary for the winter-run, which spawn in the blast-furnace heat of the Sacramento Valley’s summers.

“We see this an area that can be resilient to climate change,” said Howard Brown, the Sacramento River basin chief for the National Marine Fisheries Service.

At the end of their three-year life cycle, adult Chinook instinctively return from the ocean to the stream or river where they were hatched to spawn and die. Battle Creek was one of their traditional spawning grounds, but small hydroelectric dams and other barriers blocked the fish from using its icy waters.

It has taken nearly 20 years and close to $100 million to remove barriers and install fish ladders and screens to open up enough of Battle Creek’s northern fork for regulators to try introducing the fish to the creek in the hopes of building a self sustaining population.

Winter-run are the most critically imperiled and most at risk from a warming climate of all of the Central Valley’s three main salmon runs. The winter-run is so named because it’s during the winter months that adult fish swim under the Golden Gate Bridge, leaving the Pacific Ocean to begin their one-way journey to lay their eggs and die in freshwater.

Cut off by dams from the spring-fed, cold-water tributaries where the species used to spawn, the winter-run now lay their eggs in the heat of the summer in a short stretch of the Sacramento River below Shasta Dam in Redding.

In recent years, the run has been kept alive almost entirely by a small emergency hatchery built at the base of the dam.

The plight of the winter-run reached crisis levels during California’s historic drought, which began in 2012. Warm water below the dam those years was baking winter-run eggs and baby fish, and researchers were reporting record low numbers of juvenile fish heading down river toward the ocean.

Fishing groups, whose anglers have seen restricted fishing seasons tied in part to the decline in winter-run fish, applauded the new program.

“I think everyone agrees that we need at least one backup population of winter-run salmon in addition to the one that’s teetering on the brink of extinction in the upper Sacramento River,” Golden Gate Salmon Association president John McManus said Thursday in an emailed statement.

How successful the program is won’t be known until 2020 when the fish released over the next few weeks start to return to Battle Creek to spawn.