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Tests Find 46% of Sampled Klamath River Salmon Carry Parasite, Up From 22% Last Year
nypost.com reported that 46 percent of 696 Chinook salmon tested positive for Ceratonova shasta during the 2026 outmigration season. The rate marks an increase from 22 percent the prior year. Officials in California and Oregon are monitoring the parasite in the river system.
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com reported that officials in California and Oregon are on alert after the US Fish and Wildlife Service documented an increase in the Ceratonova shasta parasite in the Klamath River. Numerous Chinook salmon have turned up dead in large groups along the Scott and Trinity rivers, which are tributaries of the Klamath.
During the 2026 outmigration season, officials collected salmon from March 17 through May 12 and tested 696 fish.
Of those, 319 tested positive for the parasite, or 46 percent. In 2025, 39 of the salmon tested, or 22 percent, exhibited the parasite conditions. The Klamath River begins in Oregon’s high desert interior, cuts through the Klamath Mountains, and enters the Pacific Ocean in Northern California.
The parasite can affect several freshwater species and typically makes fish appear darker with swollen abdomens. The parasite is transmitted to fish through the gills by infectious actinosporean tetractinomyxon stages in the water shed by parasitized freshwater polychaete worms, according to the Alaska Department of Fish and Game.
There are no human health concerns associated with the Ceratonova shasta parasite.
