Hundreds of Thousands of Salmon Dead From ‘Gas Bubble Disease’ in US River

Mass die-off in Klamath River caused by extreme changes in water pressure amid largest dam removal project in US history

As many as hundreds of thousands of newly hatched Chinook salmon released into the Klamath River have died due to “gas bubble disease” caused by extreme changes in water pressure.

The young salmon fry were released amid the largest dam removal project in US history along the 257-mile-long river, which flows across Oregon and California. Four hydropower dams are being removed, reconnecting the lower and upper portions of the Klamath River for the first time in a century and allowing fish free passage along the river.

The removal is the result of a decades-long campaign by tribes, environmentalists and fishers to restore the river and its ecosystem to their natural state. One dam has been fully demolished and three others are scheduled to come down this year.

Last week, the California department of fish and wildlife (CDFW) released 830,000 hatchery-raised fall-run Chinook, only to discover days later that they were dying downstream of the 173ft Iron Gate dam, which is scheduled to be demolished soon. A tunnel at the dam’s base had been opened to allow the river to pass freely across it for the first time in a century, a step before the structure could be fully removed.