Hundreds of Thousands of Salmon Die After Release in Northern California’s Klamath River

The juvenile Chinook salmon likely died from pressure changes as they swam through an old tunnel in the Iron Gate Dam, slated to be removed this year as part of a massive demolition project

Lots of small fish
Wildlife officials released 830,000 fall-run Chinook salmon fry into Fall Creek. A large but unknown number of them died as they passed through a tunnel on the Klamath River. California Department of Fish and Wildlife

Hundreds of thousands of juvenile Chinook salmon are presumed dead after being released into Northern California’s Klamath River last week, where the largest dam demolition project in United States history is underway. The cause of death? Gas bubble disease, a fatal condition that results from severe pressure changes.

The incident occurred on February 26 in northern California, not far from the border with Oregon, according to a statement from the California Department of Fish and Wildlife (CDFW). On that day, wildlife officials released 830,000 fall-run Chinook salmon fry into Fall Creek, a tributary of the Klamath River. The juvenile fish had hatched at Fall Creek Fish Hatchery, CDFW’s new, $35 million facility that was approved last spring. It was the first release of juvenile fish from the new venue.

The fish were deposited into the creek above Iron Gate Dam, a hydroelectric dam that opened on the Klamath River in 1964 and is slated for removal later this year. As they made their way downstream, the salmon fry had to pass through an old tunnel that is also set to be removed—and this is where wildlife officials think they experienced the fatal change in pressure.

The catastrophe is “another sad reminder of how the Klamath River dams have harmed salmon runs for generations,” according to a CDFW statement.

Wildlife officials haven’t said exactly how many of the young fish died, only that the group “experienced a large mortality” based on downstream monitoring data.

“It was discouraging and sad to learn of this issue,” Jordan Traverso, a spokesperson for the CDFW, tells SFGATE’s Amanda Bartlett. “Our staff invest so much of their time and care into these fish; it is really tragic to have something like this happen.”

Officials found no evidence of water quality issues in the river—turbidity and dissolved oxygen levels were both “suitable” on the day of the release and the days leading up to it, according to CDFW. In addition, other types and ages of fish—yearling coho and Chinook salmon—that were swimming downstream from the dam around the same time were all healthy.

But the visual appearance of the dead fish, which had telltale bulging eyes, pointed to gas bubble disease as the culprit.

“Poor habitat conditions caused by the dams and other circumstances such as this are reasons why CDFW conducts releases of hatchery fish at various life stages,” according to the statement.

Moving forward, until the dam can be removed, wildlife officials will only release fish below the dam so the animals don’t have to swim through the tunnel. The hatchery still has roughly 3.27 million fall-run Chinook salmon, and additional releases are scheduled for later this month.

Hatchery officials want to release 1.25 million salmon fry, 1.75 million salmon smolts (slightly older fish) and 250,000 salmon yearlings this year. They should still be able to meet and, likely, exceed this goal with the remaining fish at the facility, per the CDFW.

The Klamath River starts in south-central Oregon east of the Cascade Range. From there, it snakes 263 miles through southern Oregon and northern California before reaching the Pacific Ocean near Crescent City, California. The entire Klamath River basin spans 12,000 square miles.

At one time, the Klamath was the third largest salmon-producing river on the West Coast, according to the National Oceanic and Atmospheric Administration (NOAA). But, largely due to hydroelectric dams built along the waterway between 1911 and 1962, populations of salmon and other fish that swim upstream to spawn have “declined substantially in abundance,” according to NOAA.

Now, however, plans are underway to remove four of the dams by the end of this year. The $450 million initiative, which started last fall, should, in theory, help salmon numbers rebound.

But the project has recently come under scrutiny, with some experts raising concerns about fish health as massive amounts of the previously stored sediment, unleashed by the dam removal, have flowed downstream and turned the water brown. The river’s drawdown exposed mud, which has trapped deer and revealed dead fish, mostly of non-native species such as bass and catfish.

These impacts were expected, project managers tell the San Francisco Chronicle’s Kurtis Alexander. But the recent die-off of salmon fry was unintentional.

“While the project’s going through a lot of scrutiny, this is just another thing for naysayers to pile on to,” Curtis Knight, executive director of conservation group California Trout, tells Rachel Becker of CalMatters. “But I think it’s important to note the dam is not going to be there much longer—that’s what caused these fish to die, and conditions in the river below are improving.”

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