Walbridge fire damages half of prime salmon, steelhead spawning grounds, experts say

In burning to the edge of Lake Sonoma, the Walbridge fire has posed an unprecedented threat to the water supply for 600,000 North Bay residents and scorched Sonoma County streams that are critical to the revival of imperiled fish.

Rural residents and environmentalists also are concerned the miles of bulldozer tracks left by firefighters — an essential tool in the ongoing battle against the 55,000-acre fire — could contribute to post-fire erosion, water pollution and possible mudslides when winter rains fall on barren ground.

Experts estimated that half of the spawning habitat on Russian River tributaries has been burned, dealing a potential setback to expensive, longstanding efforts to bolster the coho salmon and steelhead trout populations.

Scientists and public officials are quick to say that damage to the land and water do not rival the loss of homes, lives and property wrought by the two-week fire, which was 49% contained Saturday evening.

But there is an urgent need, they say, for experts to survey the vast fire scar over rugged hills and rural communities and then determine steps to offset added damage when winter rains soak into unstable soil.

No previous wildfire is known to have come so close to Lake Sonoma, the 54,000-acre reservoir northwest of Healdsburg that is the major source of Russian River water delivered to 600,000 customers in Sonoma and Marin counties.

The Walbridge fire burned to the edge of a roughly 4.5-mile stretch of the reservoir’s Warm Springs arm, where the denuded, ash-covered land slopes steeply toward the water.

“We have a high level of concern,” said Grant Davis, general manager of Sonoma Water, acknowledging that preventive measures must be taken. “We need to get the expertise on the ground to determine what steps are necessary.”

Absorbent straw barriers are needed on scorched slopes around the lake to help prevent ash and sediment from being swept into the reservoir, which holds about 62 billion gallons of water, he said.

The county’s water agency also is concerned that pollutants small enough to slip through the gravel bed that naturally filters the water pumped from deep below the Russian River near Forestville might force the agency to establish new treatment facilities.

In a bid for assistance, the county this week asked Cal Fire to form a watershed emergency response team to assess the hazards from the Walbridge fire and the 2,360-acre Meyers fire on the coast and recommend countermeasures.

Team reports in the wake of the 2017 and 2019 wildfires were “foundational in guiding our recovery operations,” said the letter from Chris Godley, the county director of emergency management.

For fish habitat, the immediate forecast is perhaps more bleak.

“We expect this to be quite devastating,” said Eric Larson, a state Department of Fish and Wildlife environmental program manager based in Santa Rosa.

Larson estimated that half of the spawning habitat for protected coho salmon and steelhead trout — from Dry Creek downstream along the Russian River to Austin Creek — was either burned or will ultimately be diminished by fire-related impacts.

Fish and Wildlife is just beginning post-fire damage assessments, he said, noting there have been “catastrophic fires in almost every county surrounding San Francisco Bay.”

Terrestrial wildlife also has been impacted, as predators like bobcats, raccoons and skunks have been displaced from burned woodlands and moved into rural residential areas where they are breaking into chicken coops and attacking livestock, he said.

Don McEnhill, executive director of Russian Riverkeeper, a Healdsburg nonprofit, estimated that half of the prime coho recovery habitat on six streams — Austin, Mill, Felta, Porter, Grape, Pena and Dry creeks — were in the Walbridge fire footprint.

“If you had to put a fire in a really bad place for salmon restoration and water supply, this is it,” he said.

Austin Creek flows into the Russian River at Cazadero, while all the others drain into Dry Creek, the conduit for water from Lake Sonoma that merges with the river below Healdsburg.

Coho are the most imperiled of the North Coast fish, driven nearly to extinction until the breeding program began in 1980 at the Warm Springs Dam hatchery named for Don Clausen, the former congressman who represented the North Coast for 20 years.

The hatchery aims to produce at least 300,000 steelhead that are planted each year in Dry Creek, along with 80,000 coho that are planted in streams around the Dry Creek watershed.

McEnhill, a longtime advocate for the Russian River, said wildfire heat transforms the environment, consuming the organic matter in the ground and leaving “crumbs of dirt that aren’t sticking together very well.”

Add rain and “it just doesn’t stay in place,” McEnhill said, adding that landowners are already worried about mudflows on their property that can block roads and bury streams.

Erosion from barren land can carry sediment into a stream, clogging gravel beds where salmon and steelhead spawn and smothering tiny organisms that make up the foundation of the aquatic food chain, McEnhill said.

Dirt in the water can tear apart the gills of juvenile fish, he said.

Much of the Walbridge burn area is in a geological formation that is “generally unstable,” magnifying the risk of landslides, said Jay Jasperse, chief engineer at Sonoma Water.

The area includes Venado, a remote community best known as one of the wettest places in Sonoma County and the entire West Coast, and now one of many ravaged by the fire. Heavy rain will make the land there even more unstable, he said.

In addition to the reservoir, Sonoma Water has a vested interest in the well-being of Dry Creek, having spent $30 million on habitat restoration along 3 miles of the waterway, with most of the money coming from water ratepayers, Davis said. The agency recently got another $30 million from the Army Corps of Engineers to complete the other half of the 6-mile restoration project.

At his 115-acre ranch on Felta Creek at the southern edge of Dry Creek Valley, Nick Broderick was coping with another impact: the scars left by steel blades of Cal Fire’s bulldozers that scrape the vegetative skin off the ground.

Firebreaks cut by dozers are a crucial weapon in Cal Fire’s arsenal and they have been deployed since the Walbridge blaze erupted Aug. 17, Division Chief Ben Nicholls said.

Broderick said he was happy to see the dozer that traversed his land, cutting a firebreak between Sweetwater Springs Road and Mill Creek Road. He even showed the operator the best place to drive across Felta Creek, a trickle at this time of year.

“They’re important, for sure,” he said. “I felt a whole lot better when they went in.”

But when it rains, those bare dirt tracks can become conduits for sluicing sediment into creeks.

As Cal Fire reins in a blaze, it begins “suppression repair,” which includes mending fences, fashioning humps called water bars to divert flows from dozer tracks, and smoothing out berms created as the tracks were cut, said Scott McLean, a Cal Fire spokesman.

Dozer tracks are “incredibly invasive and destructive,” said Nick Malasavage, chief of operations and readiness at the Army Corps of Engineers office in San Francisco. But, he added, they are also “essential in controlling fires,” a reasonable trade-off.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.