The department says it is presumed to be due to gas bubble disease as the fry migrated through the Iron Gate Dam tunnel.
Bubble disease results from environmental or physical trauma often associated with severe pressure change.
It was an estimated 830,000 fall-run Chinook salmon fry that were released from the new Fall Creek Fish Hatchery on February 26.
This was part of California’s ambitious $35 million initiative to restore Chinook and coho salmon populations along the undammed portions of the river.
Monitoring downstream revealed the mass mortality, indicating the outdated Iron Gate Dam infrastructure as a significant factor. However, the CDFW noted that the water quality in the Klamath River appeared stable and suitable for the salmon’s health, ruling out other potential causes for the die-off.
The CDFW says future releases will occur below the dam until the infrastructure improvements are made. Despite the setback, CDFW’s Fall Creek Fish Hatchery says it is exceeding annual production goals with around three and a quarter million healthy fall-run Chinook salmon ready for future releases, some of which are planned later in the month.
