California’s fifth largest wildfire is encroaching on some of the last strongholds for imperiled salmon, with potentially devastating consequences for a species already on the brink.

The explosive Park Fire has spread into the Mill and Deer Creek watersheds in Tehama County, which are two of the three remaining creeks where wild, independent populations of spring-run Chinook, a threatened species, still spawn in the Central Valley.

If the Park Fire climbs to higher altitudes, federal and state officials said it could strike the final deathblow to the region’s spring-run salmon, which are already at risk of extinction.

“It’s really concerning. It’s really sad. Spring-run Chinook populations have taken such a hit over the past few years, and they’re just at a critically low point,” said Howard Brown, senior policy advisor with the Central Valley office of the National Oceanic and Atmospheric Administration’s West Coast fisheries region. “The emotional toll of seeing a fire like this hit such an important place, with (critically at-risk) populations that are suffering so bad, it just feels like the cards are stacked up deeply.”

Experts are anxiously awaiting the wildfire’s next move, hoping that it doesn’t spread farther into higher elevations. That’s where adult salmon are waiting in cool pools for water temperatures to drop and flows to rise so they can spawn, and where year-old juveniles are gaining strength before migrating to the ocean.

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“We’re kind of at the mercy of the weather and wind to see if these fires creep along doing beneficial to less-severe things, or if we see a big run that really cooks the watershed,” said Matt Johnson, a senior environmental scientist with the California Department of Fish and Wildlife Northern Region Anadromous Fisheries Program.

“The species is at real risk of extirpation or blinking out. We hope that doesn’t happen,” he said.

Flames are not the primary, immediate threat. The spring-fed streams are moving so fast that ash in the water will quickly wash away, according to wildlife officials. Instead, firefighting efforts could pose a direct threat to the waterways, including the use of fire retardant, which is toxic to fish, though experts say it’s a necessary tradeoff.

“The important thing right now is to just try to stop it on the head, so it doesn’t burn up these really precious watersheds,” Brown said. “The next few days will be pretty telling.”

The most severe damage could come later this year — if heavy rains wash ash, chemicals and sediment from the burn scar into the creeks. Too much sediment can smother the eggs and baby fish, or spark a microbial bloom that sucks oxygen from the water. Larger debris flows also could scour the waterways and fill in holding pools.

“It’s like liquid cement coming down the river channel,” said Steve Lindley, director of fisheries ecology at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center lab. “It just scours the river down to the bedrock, and everything in it is crushed and ground up.”

Two years ago, flash floods sent debris from Siskiyou County’s McKinney Fire into the Klamath River, where the Karuk Tribe reported a devastating fish kill.

Protected by the nation’s Endangered Species Act since 1999, Central Valley spring-run Chinook have already experienced catastrophic declines, reaching record lows last year with only 16 adults returning to spawn in Deer Creek and 34 to Mill Creek. These populations, the California Department of Fish and Wildlife warned earlier this year, “are now at high risk of extinction.”

“To see really big, hot fires like this move into what used to be their strongholds — it’s really a tough thing to witness,” Brown said. “Right now, it feels like the frontlines of climate change.”

Salmon ‘are really struggling’

Spring-run Chinook salmon were once the cornerstone of California’s commercial fishery, with more than half a million fish caught in 1883 alone.

But California’s big dam era in the 20th century also sparked a massive decline of spring-run Chinook, one of the four runs of salmon named for the season when they return to freshwater to spawn. The dams cut off critical upstream spawning habitat, shifted the timing of flows and degraded downstream waterways.

Now nearly all of the Central Valley’s spring-run populations are gone. The remaining ones are largely confined to the northern Sacramento Valley, where Mill and Deer Creeks provide some of the last, high quality, high-elevation habitat for the species, as well as for threatened Central Valley steelhead.

Both are tributaries to the Sacramento River. Born in Lassen Volcanic National Park, Mill Creek flows through forests and meadows before dropping through a steep rock canyon into the Sacramento Valley, where it meets the Sacramento River. Deer Creek emerges near the summit of Butt Mountain, flowing 60 miles before it reaches the valley floor and stretches another 11 miles to join the Sacramento River near Vina.

“Deer and Mill Creeks have always represented this exceptional habitat piece for salmon,” said Johnson. “Unfortunately, despite that great habitat, the fish populations are really struggling.”

Last year, counts of returning adults were so low, scientists described it as a cohort collapse — meaning there were too few to successfully produce a new generation. The catastrophic declines prompted state and federal wildlife agencies to begin a conservation hatchery program at UC Davis.

The program was in response to the “threat that this species could blink out because nothing would return in subsequent years. So the captive brood population is like a little insurance plan or bank account of genetic material,” Johnson said.

With so few returning adults, a hit to the next generation from the Park Fire could be catastrophic. Johnson said after the Dixie Fire in 2021, he saw the first rains of the season turn Mill Creek black with runoff.

“The adults returning this year are from that Dixie Fire cohort and we’re looking at preliminary very low returns,” Johnson said. Though he doesn’t have the evidence yet to back it up, the fire “could be a contributing factor.”

State wildlife officials in February warned water regulators that the fish have been in steep decline since 2015 — in part because agricultural water diversions from the lower rivers frequently drain the creeks. They urged the State Water Resources Control Board to set minimum levels of water that must flow through the creeks to protect fish.

“Historical water diversion and water use practices have long been out of balance with ecological needs on these critical watersheds,” Tina Bartlett, regional manager of the northern region, wrote to the water board. In recent years, the problem has been amplified by climate change and frequent droughts.

Water board staff are reviewing the recommendations, according to spokesperson Ailene Voisin.

Eggs and young fish could be smothered

Because of the fire, state wildlife officials cannot survey the number of adult salmon that returned this year, Johnson said. But preliminary estimates for this year remain very low — prompting alarm from scientists.

“We had a really bad year last year. We had a really bad year this year,” said Andrew Rypel, director of the Center for Watershed Sciences at UC Davis. “Say we wipe out this cohort. Salmon are on a three-year lifecycle. That’s starting to look like the anatomy of an extinction.”

The wildfire is not an imminent threat to adults that are in the creeks right now, Johnson said. The creeks have abundant cool water, and as of Monday the fire was not affecting flow or temperatures.

“What this fire represents, if it were to consume the habitat in the upper watersheds, is a degradation of that habitat. It’s just another hit to the species that’s already struggling,” Johnson said.

In these fire prone landscapes, low-intensity fires can be beneficial. Some sediment in the water can help hide juveniles from predators. Downed trees in the stream can create fish habitat.

But Johnson and others are concerned about the heat and intensity of the fire. If the first rain events send mud and ash flooding into the creeks, the eggs or juveniles could be smothered by the sediment, or suffocate if oxygen levels plummet. Chemicals could degrade the water quality.

Brown said that these hot fires could reshape this wild, remote landscape. Recent studies show that the one-two punch of climate change and severe fires can change which plants return to a fire-scoured region. Denuded slopes are primed for erosion, and the loss of tree cover could allow these vital, cool stretches of river to warm in the summer.

“At this point, my greatest concern is the fire moving any further up Mill and Deer Creek. A hot fire blowup could have devastating ecological consequences for the watershed health of these streams,” he said. “The watersheds and the salmon are irreplaceable resources in the state of California and they are almost gone. This hurts.”

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This story was originally published by CalMatters and distributed through a partnership with The Associated Press.

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