Mass Salmon Death in California From Gas Bubble Disease

Hundreds of thousands of fish have died in California’s Klamath River from suspected gas bubble disease, a condition caused by a change in water pressure.

The California Department of Fish and Wildlife (CDFW) released 830,000 chinook salmon fry into the river, near the Iron Gate Dam, at the end of February — as part of an initiative by the department to boost both coho and chinook salmon populations in the river.

However, officials believe that the salmon were subjected to severe pressure changes, leading to gas bubble disease, while passing through the Iron Gate Dam tunnel.

Gas bubble disease occurs when an over saturation of nitrogen or other gases in the water is consumed into the body.

Fish with the disease typically display signs of disorientation, and will swim near the surface of the water. Their skin also darkens, and hemorrhages are likely. The disease comes with a high mortality rate.

“The salmon fry experienced a large mortality, based on monitoring data downstream,” a statement from CDFW said.

“Indications are the cause of mortality is gas bubble disease that likely occurred as the fry migrated though the Iron Gate Dam tunnel, old infrastructure that is targeted for removal along with the Iron Gate Dam itself later this year.”

The department said that, so far, there is no evidence to suggest the deaths were caused by any other factors relating to water quality.

Other potential reasons for the death of the fish could be dissolved oxygen or turbidity. However, these were both tested before the salmon were released into the river and found to be at suitable levels.

Officials noted that healthy chinook and coho salmon were found coming from further downstream.

“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,” the CDFW said in a statement.

“CDFW will plan all future salmon releases below Iron Gate Dam until this infrastructure is removed.

“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.”

The salmon were bred in CDFW’s Fall Creek Fish Hatchery, a recent investment that currently holds 3.27 million fall-run Chinook salmon. The department reported that more releases are planned later in the month.

“The annual fall-run Chinook salmon production goal for the hatchery is to raise and release 3.25 million fish—1.25 million released as fry, 1.75 million as smolts, and 250,000 as yearlings,” the department reported.

“The additional stock of fall-run Chinook salmon remaining in the hatchery exceeds the annual production goal and will help offset losses experienced with the initial release of fry.”