Science Spotlight

A healthy steelhead trout surveyed at Pescadero Creek Lagoon Complex in 2017


The aftermath of a winter sandbar breach 2014. These nearly annual breaches resulted in large die-offs for the lagoon’s steelhead.


A manual breach of Pescadero Creek Lagoon Complex. Managed breaches of the lagoon can prevent fish kills caused by turbulent natural breaches. Photo Courtesy of UC Davis School of Veterinary Medicine

There’s a dichotomy in the way Pescadero Creek Lagoon Complex in coastal San Mateo County has both supported—and been detrimental to—steelhead trout for much of the past 25 years.

On one hand, the lagoon complex—the largest tidal marsh between Elkhorn Slough and the San Francisco Bay estuary—boasts high growth rates for Central California Coast Steelhead. The lagoon system allows the species, which is federally listed as endangered, to reach a size that increases their likelihood of surviving at sea. Steelhead also use the system for juvenile rearing and resting during migration.

On the other hand, nearly every year since the mid-1990s, the lagoon faced harsh fall/winter sandbar breaches that filled the system with oxygen-depleted water and spread toxic sediment produced by the breakdown of organic matter like plant material in the absence of oxygen.

These breaches often resulted in large die-offs for the lagoon’s steelhead population. Historically, population estimates have reached as many as 17,000 steelhead rearing into the fall.

“It was a one-two punch where fish faced lack of oxygen and got hit with harsh toxic compounds. It was really unfortunate because the lagoon system works so well to grow steelhead, but we were losing the production every year,” said District Fisheries Biologist Jon Jankovitz.

Efforts to actively manage breaches began in 2012, but were stalled in 2014 and 2015 when the steelhead population was diminished due to drought conditions. In 2015, the California Department of Fish and Wildlife (CDFW) and the National Oceanic Atmospheric Administration (NOAA) partnered with the Department of Parks and Recreation (DPR), which owns much of the land associated with the complex, in adopting a monitoring and management plan.

In 2016, a significant fish kill caused by a turbulent sandbar breach prompted further action. CDFW, NOAA and DPR resumed active management to improve water conditions and prevent the deadly breaches.

The restoration team installed a sandbar dam at a major channel to slow the release of oxygen-depleted water and sediment into the system. Staff also preemptively manually breached the lagoon mouth on occasions when they anticipated a harmful natural breach.

Jankovitz conducts weekly water quality monitoring and twice-monthly dry-season fish sampling to inform management decisions. He produces an annual report on the health of the steelhead population and a summary of seasonal water quality transitions.

So how has active management faired? There hasn’t been a significant fish kill since 2016.

“We’ve saved the steelhead population for the last couple of years. We’re fortunate for the success we’ve had so far,” said Jankovitz.

Another mark of success has been the documented presence this year of sexually mature holdovers, meaning steelhead that were reared in the lagoon for two seasons even though they were large enough to smolt (i.e. migrate to sea).

“This obviously couldn’t happen if there was a fish kill the year prior. These holdovers represent a life history strategy that may fill in gaps during down reproductive years or periods of poor ocean conditions,” said Jankovitz.

There’s a long-term restoration plan in the works which would likely involve structural changes, such as relocating culverts and breaching levees, to alter the dynamics of how much tide flows in and out of the system. The plan includes a sediment removal project that was implemented in 2019 to increase fish passage.

Ultimately, CDFW and DPR would like to keep the system thriving without active management. “We don’t love breaching the lagoon manually because it can be stressful for fish and other aquatic species,” Jankovitz said.

Meanwhile, fostering an environment in Pescadero Creek Lagoon Complex that supports a large population of fast-growing steelhead continues to be top priority.

“Aside from being a native California species with a long history of recreational and angler use, steelhead are a great biological indicator of the health of streams and lagoon systems. The ecology of these systems would likely fall apart without them,” Jankovitz said.

Photos courtesy of CDFW District Fisheries Biologist Jon Jankovitz and the Bodega Marine Lab at University of California, Davis. Top Photo: District Fisheries Biologist Jon Jankovitz with a healthy Pescadero juvenile steelhead.

Media Contact:
Ken Paglia, CDFW Communications, (916) 322-8958

Faded black and white photos are all that’s left of the Owens River Gorge’s glory days as a trophy brown trout fishery. Biologists expect the fish to make a comeback following near-annual pulse flows that begin in September to improve habitat.




CDFW crews electrofish the Owens River Gorge two times per year to assess the health of the river’s brown trout.

From boom to bust to decades of angler indifference, few California fisheries have experienced such wild swings of fortune as Mono County’s Owens River Gorge.

The latest chapter in the long saga of the Gorge unfolds this month when the Los Angeles Department of Water and Power (LADWP) sends a relatively brief burst of water known as a “Channel Maintenance Flow” down the 10-mile stretch of river between the Upper Gorge Power Plant and Pleasant Valley Reservoir to benefit fish habitat.

From Sept. 9 to Sept. 17, water flows will rise from the relatively placid 35 to 55 cubic feet per second (cfs) typical in the Gorge to 680 cfs before gradually ramping back down. Access to the Gorge will be closed by LADWP during the nine-day “pulse flow” event for public safety.

The temporary boost in water flow represents the successful resolution of decades of legal battles involving LADWP, Mono County and CDFW. The high flows are expected to breathe new life into the Owens River Gorge ecosystem and its once-storied brown trout fishery. Court settlements mandate the pulse flows continue almost annually -- 18 out of every 20 years.

The flows are intended to replicate seasonal scouring that occurred naturally in the Gorge long before dams, power plants and water diversions were constructed in the last century. In fact, these alterations dried up the Owens River Gorge from 1953 to 1991 until years of litigation restored some minimal flows and attempts to restart a once-fabled brown trout fishery.

The Owens River Gorge is paradoxical – so close yet so far away. Just northwest of Bishop and within sight of Highway 395, it is difficult to access with limited and steep trails to reach its waters 500 to 900 feet below the rim. Since water returned to the Owens River Gorge in 1991, it has been more popular with hikers and rock climbers than trout anglers.

It was a much different story prior to the construction of the Long Valley Dam in 1941, which created Crowley Lake, and the subsequent addition of a number of power plants along the stretch of river. Before then, the Owens River Gorge was a destination brown trout fishery with a worldwide reputation. So good was the fishing it was one of the few waters in California with limits based on weight – 25 pounds plus one fish per angler per day.

CDFW Environmental Scientist Nick Buckmaster is based in Bishop and conducts twice-yearly electrofishing surveys in the Gorge along with macroinvertebrate sampling.
“Right now, the fish populations are pretty stunted,” Buckmaster said. “We just don’t have large brown trout in the Gorge anymore.”"

The Gorge is home almost exclusively to wild brown trout and the populations are high. Buckmaster estimates between 1,500 to 5,000 trout per mile, numbers that compare favorably to many blue-ribbon trout fisheries in the state.

“The problem is they are all small. Their growth really slows down around 5 inches, and most of the fish in the Gorge are less than 8-inches long. Their growth really plateaus,” he said. “By the time they get to 8 inches, they are geriatric fish.”

Buckmaster explained that brown trout undergo an important life change once they reach between 8 and 14 inches in size. They mostly stop eating aquatic insects and transition into apex predators, preying on other fish and just about anything else of substance they can eat. The diet change leads to rapid growth and turns them into a prize for any trout angler skilled enough to catch them.

Plateauing at 5 inches, however, most of the brown trout in the Owens River Gorge never reach that important developmental milestone or achieve it only toward the end of their lives.

“If you want big brown trout, they need something to eat,” Buckmaster said. “And they usually need a lot of something to eat.”

CDFW fisheries biologists expect the pulse flows to provide just that by dramatically altering the ecosystem. The big burst of water will scour pools and restore the deep-water holding and ambush habitat needed by large brown trout. The flows will flush out years of accumulated sediment, exposing gravel beds critical for trout breeding while fostering a broader diversity of aquatic life than what’s present in the Gorge today.

Mayflies and stoneflies are largely absent from the ecosystem, and caddisflies – safely encased and underneath rocks in their larval stages – provide a limited food source. Small populations of native Owens suckers exist in the Gorge. Their numbers are expected to grow with an increase in aquatic insect life following the pulse flows, incidentally providing important forage for growing brown trout.

The high waters will inundate and benefit riverside riparian growth, offering shade and cover and additional insect habitat. The flows also are expected to flush out invasive  New Zealand mud snails that have infested the Gorge over time. The snails provide little benefit to fish and are a source of competition for other macroinvertebrate life.

Buckmaster said biologists could see positive changes in the Gorge as quickly as three months after the flows. And bigger brown trout could start turning up in Buckmaster’s electrofishing surveys – and at the end of anglers’ lines – as early as next year.

CDFW Photos. Top Photo: CDFW scientific aids Christi Kruse and Emma Hewitt identify some of the macroinvertebrate life taken from the Owens River Gorge.