By Robin Meadows
Two years ago, California’s winter-run chinook were dealt a devastating blow. These endangered salmon were already struggling to survive, with as few as one thousand adults returning from the ocean to spawn in recent years.
Then, in 2021, a sizzling summer on top of a severe drought killed three quarters of the eggs the fish laid in the Sacramento River near Redding, their last remaining spawning grounds. Now, a new plan to help protect winter-run chinook eggs is in the works.
Named for the season they swim upstream, winter-run chinook wait as late as August to spawn. Summer temperatures in the Central Valley regularly soar above 100 ⁰F, making it a challenge to provide the cold water that salmon eggs require. During the summer of 2021, there simply wasn’t enough cold water left in Shasta Lake to keep the river below the 53.6 ⁰F limit required to protect their eggs.
Saving some of Shasta Lake’s water from one year to the next would help. “We need to ensure end-of-September storage as an insurance policy in case the next year is really dry—that would have avoided the catastrophic mortality we saw in 2021,” says Doug Obegi, Director of California River Restoration at the Natural Resources Defense Council, adding that winter-run egg deaths have been devastatingly high in three of the last 10 years. September marks the end of the water year in California, which has a Mediterranean climate with dry summers and wet winters.
Historically, spawning in the summer was no problem for winter-run chinook. These fish once swam to high elevation tributaries of the Sacramento River, which were fed by snowmelt and cold water springs from Mount Shasta. But this upstream access was blocked by the 1945 completion of Shasta Dam, which the U.S. Bureau of Reclamation built and operates.
Today all adult winter-run chinook lay their eggs in a 10-mile stretch below the dam. Fish biologists think of this as the salmon wanting to get as close as possible to their historical spawning grounds.
TEMPERATURE CONTROL
While winter-run chinook initially rebounded from the impact of dam construction, reaching nearly 120,000 adult spawners in 1969, they plunged to a low of 186 spawners in 1993. These salmon were listed under the federal Endangered Species Act in 1989, and the first temperature standard for their spawning grounds was set in 1990.
Meeting that standard often depends on releases from Shasta Dam. Cold water sinks, so the water that winter-run chinook eggs need in the summer collects in the deepest parts of Shasta Lake. But the bottom of the reservoir is also the location of the pipes that feed Shasta Dam’s hydropower turbines, which meant that power generation could spill the coldest water before the fish had even arrived to spawn.
In an effort to both produce hydropower and save cold water for salmon, the U.S. Bureau of Reclamation installed a box-like structure on the dam’s inner face in 1997 to regulate the temperature of releases.
This structure, called a temperature control device (TCD), spans the height of the 602-foot-tall dam and is equipped with a series of gates from top to bottom. Because the gates are at different heights, they can be opened and closed selectively to draw from different depths—and so different temperatures—of the water in the reservoir.
Crucially, releases can be drawn from the warmer water at the top before winter-run chinook arrive to spawn, saving the cool, deep water their eggs need to get through the hot summers.
“If we didn’t have the TCD, we’d be at risk of releases with significantly warmer temperatures from July to October,” says Kristin White, who is Deputy Regional Director at the Bureau of Reclamation and until May of this year was operations manager for the Central Valley Project, which includes Shasta Lake and Dam. “Our best guess is we’d see temperatures upwards of 60 to 65 ⁰F.”
BACK-TO-BACK DROUGHT YEARS
Of course, for the temperature control device to work, there has to be cold water in Shasta Lake in the first place. And cold water was scarce in 2021, which was California’s second drought year in a row and hottest summer on record.
“It was by far the driest year on record at Shasta; it was really bad, something we’d never seen before,” White says, adding that as bad as it was there, it was even worse at other reservoirs. “We were doing relatively well so we got pulled to help elsewhere; everyone was struggling.” Shasta Lake is the state’s largest reservoir with a capacity of 4.5 million acre-feet, enough for up to nine million California households per year.
“We got through 2021 at the expense of cold water storage,” White continues. And at the expense of winter-run chinook.
Then came 2022, the state’s fourth driest on record. “Having the fourth driest right after the driest was not a good combination,” White says. “We had to make really difficult decisions.”
To save cold water in Shasta Lake for salmon, the Bureau of Reclamation slashed water deliveries by more than 80% to Reclamation District 108, a consortium of 130 water users with senior rights to the Sacramento River. Reclamation District 108 supplies irrigation water to nearly 48,000 acres of farmland in Colusa and Yolo counties.
“It was devastating to the whole community,” White says.
The 2022 water cuts fallowed more than 370,000 acres in the Sacramento Valley, causing an estimated $1.3 billion in agricultural damages and the loss of 14,300 jobs, according to a report by UC Davis agricultural economists Daniel Sumner and William Matthews.
“Our communities are all agriculture; there aren’t really any other jobs,” explains Reclamation District 108 General Manager Lewis Bair. “If we lose people, there’s nothing to bring them back—it’s a death spiral.”
Low Sacramento River flows can also threaten the giant garter snake, a federally threatened species that lives in Central Valley wetlands and waterways as well as irrigation canals and rice fields. And the hundreds of bird species that migrate seasonally along the Pacific Flyway depend on flooded agricultural fields to help replace the once-extensive Central Valley wetlands, which are now all but lost to development.
PLANNING FOR DROUGHT
Both the Bureau of Reclamation and Reclamation District 108 want to move beyond crisis management of water during dry years. “Unfortunately, the writing is on the wall and drought is not going away,” White says. “How can we be better prepared?”
In a June 2023 story map, the Bureau proposes saving a larger pool of cold water in Shasta Lake from year to year as a hedge against future droughts. For its part, Reclamation District 108 is considering an upfront agreement to water cuts during back-to-back critically dry years, when the Bureau would be unable to both store cold water for the following year’s salmon and fully honor the District’s water rights.
More water in Shasta Lake is not a panacea, however, because it won’t necessarily be cold. The reservoir typically fills with runoff from rain, not snow, and storm temperatures vary. “Whether we have enough cold water depends on the weather,” White says. For example, December storms tend to be colder while March storms tend to be warmer.
Another consideration is that the needs of winter-run chinook extend far beyond cold water in Shasta. “It’s not just 10 miles of spawning habitat,” says Josh Israel, a Bureau of Reclamation fish biologist.
Salmon also need suitable habitat and enough to eat across their range from streams to the ocean, and throughout their life cycle from eggs to adults. For winter-run chinook, there are many unknowns. “It’s one of the best studied salmon and there’s still a lot of uncertainty over what’s impacting them,” Israel says.
Bair also hopes to see more protections for salmon throughout their habitats “from the ridgetop to the river mouth.” Examples include returning winter-run chinook to their historical high-elevation spawning grounds as well as reconnecting the Sacramento River with floodplain nurseries for the young fish.
“It’s just crazy to me that California doesn’t have a comprehensive package for salmon recovery,” Bair says, adding that the focus should go beyond not killing fish. “We need a new way forward.”
