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Large number of 830,000 salmon fry die after released into California river

There was a “large mortality” of the salmon fry due to “gas bubble disease” as they went through a tunnel in a dam in the Klamath River, officials said.

A large number of around 830,000 salmon fry released into Northern California’s Klamath River are believed to have died after they suffered gas bubble disease, state wildlife officials said Monday.

The condition is caused by a severe change in pressure. It happened as the fish went through the Iron Gate Dam tunnel, the California Fish and Wildlife Department said.

The tunnel and the dam of the same name will be removed later this year.

The around 830,000 Chinook salmon fry were the first release from the Fall Creek Fish Hatchery, which was a $35 million project designed to support salmon populations in the Klamath River once it is fully undammed, the wildlife department, known as the CDFW, said in a statement.

Juvenile Chinook salmon swim in a raceway at Iron Fish Gate Hatchery, Siskiyou County, Calif.,
Juvenile Chinook salmon swim at Iron Fish Gate Hatchery in Siskiyou County, Calif., before their relocation to the Fall Creek facility in 2021.Travis VanZant / California Department of Fish and Wildlife

The fish were released Feb. 26.

How many of the around 830,000 fry died was not clear, a spokesperson for the department said, but it is being called a “high mortality rate.”

There is no indication of water quality problems in the river, which is almost 270 miles long and travels from Oregon and through Northern California, and other healthy yearling coho and Chinook salmon came from downstream from the dam, the CDFW said.

From now on until the dam and the tunnel are removed, any other releases will be carried out downstream of it, the department said.

The Klamath River was once the third-largest salmon-producing river on the West Coast, and dams contributed to the decline since then, according to the National Oceanic and Atmospheric Administration.

The deaths of the fish are “yet another sad reminder of how the Klamath River dams have harmed salmon runs for generations,” the CDFW said.