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Hundreds of thousands of juvenile Chinook salmon die in Klamath River while moving through dam

Water flowing out of a tunnel at the base of Iron Gate dam on Jan. 11, 2024. Releasing water from the reservoir above was a major milestone in removing the Klamath River dams.
Ren Brownell
Klamath River Renewal Corporation
Water flowing out of a tunnel at the base of Iron Gate dam on Jan. 11, 2024.

Approximately 830,000 fall-run Chinook salmon fry are believed to have died while passing through the lowest dam on the Klamath River in late February.

Hundreds of thousands of juvenile salmon are believed to have died in late February after being released into the Klamath River from the Fall Creek Fish Hatchery on Monday, Feb. 26, according to the California Department of Fish and Wildlife. Fall Creek is a tributary of the Klamath River.

The fish were believed to have been killed as a result of gas bubble disease while passing through a tunnel at the base of Iron Gate Dam, the lowest of four dams being removed on the river. Fall-run Chinook salmon are not endangered or threatened. They died according to monitoring data downstream of the dam.

"This hurts. It's not good. As far as the actual populations, this is not going to harm the populations," said Jordan Traverso, the deputy director of communications, education and outreach for the California Department of Fish and Wildlife.

According to Traverso, the fish that perished were in excess of the numbers the hatchery had expected to produce, so their overall production is still on target.

Gas bubble disease occurs because of “environmental or physical trauma often associated with severe pressure change,” according to a March 2 press release from CDFW. The condition causes bubbles in the bodies of fish and their eyes to pop out. According to Traverso, environmental conditions in the river were good when the fish were released, and no one anticipated gas bubble disease being a problem as the fish swam through the recently opened tunnel.

The agency said the mortality does not appear to be related to turbidity or dissolved oxygen water quality conditions in the river, brought on by decades of sediment washing downstream after the dams were breached. Both turbidity and dissolved oxygen were recorded at “suitable levels” before the fish were released. Other healthy coho and Chinook salmon were documented downstream of the dam, the agency said.

“The problems associated with the Iron Gate Dam tunnel are temporary and yet another sad reminder of how the Klamath River dams have harmed salmon runs for generations,” reads the CDFW press release.

The Klamath River was once the third largest salmon-producing river on the West Coast. Dubbed the largest dam removal in U.S. history, the project on the Klamath River is taking place largely to improve salmon populations which have plummeted since the dams were first built. So far, one dam has been fully removed and three more will be deconstructed over the course of 2024. The removal of the remaining three dams will open up 400 miles of salmon habitat that's been blocked for decades.

The fish mortality incident comes at a sensitive time in the dam removal process. The recent drawdown of three large reservoirs behind the dams have exposed vast stretches of sticky mud that led to a number of deer being trapped, some of which were euthanized by CDFW. Large numbers of mostly non-native fish have also been documented dead on the shores of the river after the reservoirs were drained. Both incidents caused outcry from local residents.

According to CDFW, the 830,000 juvenile salmon killed over the past week can be buffered by the 3.27 million healthy fall-run Chinook salmon that are still at Fall Creek Fish Hatchery. The new $35 million CDFW hatchery was built as part of the long-term plan to help restore salmon runs on an undammed Klamath River. The additional fall-run Chinook “will help offset losses experienced with the initial release of fry,” the CDFW statement reads. To avoid future problems, the agency says salmon releases from the hatchery will take place below Iron Gate Dam until after the dam infrastructure is removed later this year.

Erik Neumann is JPR's news director. He earned a master's degree from the UC Berkeley Graduate School of Journalism and joined JPR as a reporter in 2019 after working at NPR member station KUER in Salt Lake City.