magine you’re a fish. A coho salmon, to be specific. Your every instinct is telling you it’s time to migrate upstream from the ocean to spawn in the rivers and streams beyond. But instead of reaching those mountain tributaries and completing your life cycle, you’re blocked at every turn.
The gateway to your spawning grounds has closed.
That’s how Kellyx Nelson describes the predicament for coho in Butano Creek, a stream just outside the tiny farming town of Pescadero on the San Mateo County coast.
“A year or two ago I walked down the creek with my waders on and all of a sudden you're walking uphill and you're on land,” Nelson said. “The creek was gone.”
Lower Butano Creek had been clogged by a mile-and-a-half long plug of sediment where the stream once flowed through the marsh to meet the ocean.
Over one stretch, a forest had grown.
Nelson says the blockage was the result of nearly two centuries of farming, logging and re-engineering the local streams, all of which triggered severe erosion.
Dirt from upstream bled into the creek and washed down to the area near town, where the stream flattens out.
“There's more than 10 miles of spawning and rearing habitat in that watershed that has been lost,” Nelson said. “We basically caused a dam to be formed so that the fish could almost never get upstream.”
In June, the resource conservation district, in partnership with California State Parks and the National Oceanic and Atmospheric Administration, embarked on a $7 million restoration project to remove the sediment dam blocking Butano Creek.
The hope is the restoration can reconnect coho with their historic spawning range upstream in Butano State Park and ultimately aid in the species' recovery.
A Species in Decline
Coho once thrived in California’s coastal rivers and creeks from Santa Cruz County to the Oregon border. Like other salmon, coho are known for what Nelson calls "this extraordinary life story."
They begin life in freshwater streams, where they spend more than a year rearing until they make their way to the ocean. Typically, after a year and a half in salt water, they return to their home creeks and rivers to spawn, then die.
Like other salmon species, they're known for their physical transformation from silver to various shades of crimson when they re-enter to reproduce.
"They're gorgeous and charismatic and mysterious,” Nelson said.
But California’s coho, once numbering in the hundreds of thousands, have disappeared from a large part of their range. South of the Golden Gate, the species is virtually extinct.
Habitat loss is a major factor driving the decline.
The Butano Creek restoration aims to solve another problem created by humans re-engineering the local landscape: frequent die-offs of threatened steelhead, which once thrived in the watershed.
These fish — ocean-going rainbow trout — spawn in nearby Pescadero Creek and grow large as they feed in the adjoining marsh. But here they face what amounts to a death trap before they can migrate into the Pacific.
Biologists believe the steelhead suffocate when they encounter stagnant, oxygen-depleted water that has formed in deep pits excavated in the marsh over the years.
This anoxic water, which engulfs the fish as it rushes out of the marsh with the first storms of the rainy season, is thought to be responsible for killing thousands of steelhead over the last few decades.
The restoration project is addressing the problem by using the sediment removed from Butano Creek to fill the pits in the marsh. That should reduce or eliminate the volume of anoxic water there and improve conditions for fish.
Local support for the project was bolstered by another consequence of the dam blocking Butano Creek: flooding on Pescadero Creek Road, the main road in and out of town.
“When it rains, people get anxious,” said Nic Erridge, who chairs the Pescadero Municipal Advisory Council.
Erridge says any time there's a big rainstorm, the road and surrounding farmland are inundated.
“It becomes a wetland,” Erridge said, “Water just flows through, the creek just spreads out.”
As a result, locals are stranded, sometimes unable to reach homes, jobs and school. Nearby farms, which help drive the town’s economy, are damaged.
“Solving this flooding issue is huge,” Erridge said. “Hopefully this project is really gonna help us.”
‘Resetting the Baseline’
For five months this summer and fall, crews used pontoon excavators, bulldozers, and dredge pumps to dig out the dirt, muck and debris from Butano Creek. Nearly 70,000 cubic yards of sediment were removed, and the stream now flows continuously from the Santa Cruz Mountains to the ocean.
Joe Pecharich, a fisheries biologist with the NOAA Restoration Center, says he sees the restoration project as “resetting the baseline” for Butano Creek.
Wildlife officials estimate the Pescadero-Butano Creek watershed has the potential to support 2,300 spawning coho and similar numbers of steelhead.
“So it really could provide an opportunity to really jump-start some recovery of coho south of the Golden Gate,” Pecharich said.
If coho don’t naturally return to the system, he says, fish could be transplanted from other watersheds or breeding programs.
What those fish will find is a creek that is still hospitable to their kind. For instance, the stream features the type of gravel female coho need to dig their nests. In these burrows, they can deposit up to 3,000 eggs. The stream and marsh can also provide young salmon the natural protection and food they need to fuel their journey into the ocean.
According to Pecharich, reopening Butano Creek for coho could also benefit the greater coastal ecosystem.
When coho and other salmon spawn, their bodies break down, feeding the surrounding environment. Birds, foxes and other scavengers feed on the fish carcasses and distribute them on land.
Pecharich says scientists now understand that salmon streams have contributed to the growth and health of redwood forests.
“It’s definitely no coincidence that coho and the range of the species extends to pretty much the range of the redwoods,” Pecharich said. “They've actually found marine-derived nutrients within these trees, which is pretty amazing.”
In turn, the trees shade and nourish the streams for fish. Pecharich says that type of exchange could happen upstream in Butano Creek, where it ends up in the redwood groves of Butano State Park.
Signs of Life
It’s too early to tell if coho will return to Butano Creek in large numbers, or if removing the sediment dam will prevent the road from flooding.
But Kellyx Nelson says there are already signs of life returning to the stream.
“The other day, about a mile and a half from the ocean, we saw a Dungeness crab. Right there in this creek, which had previously been completely disconnected,” she said.
That means as California's first big winter rains arrive, signaling the remaining Central Coast coho to begin their spawning migration, they’ll have one more path upstream.
Get the best of KQED’s science coverage in your inbox weekly.