Over 75,000 Birds Killed in North California Lake Disease Outbreak

More than 75,000 birds have died after an outbreak of disease at a North California lake.
The Tule Lake National Wildlife Refuge in the Klamath Basin, near the California-Oregon border, is in the throes of a botulism outbreak, which has killed between 75,000 and 80,000 birds.
This is now the worst outbreak in the region’s history, having killed more birds than the last such event in 2020, with thousands more expected to die in the coming weeks.
Samples from the lake tested positive for avian botulism on August 23, the Agriculture Department National Veterinary Services Laboratory has confirmed.
Avian botulism is a disease caused by a toxin produced by the bacteria Clostridium botulinum that affects birds, primarily waterfowl and shorebirds. The neurotoxin disrupts nerve function, leading to paralysis and, in severe cases, death due to respiratory failure or drowning.
Clostridium botulinum thrives in oxygen-poor environments, like mud or decaying vegetation, which are common in wetlands and stagnant water bodies. Birds typically ingest the toxin by eating contaminated food, such as fish or invertebrates, or by consuming water containing the toxin. Avian botulism outbreaks are common during warm weather when water levels decrease and decomposition increases.
Birds affected by botulism may appear weak, unable to fly or walk, and exhibit paralysis, especially in the legs, wings, and neck.
“On September 15, I saw approximately 500 dead birds in the water, from waterfowl to shorebirds to gulls to songbirds,” Teresa Wicks, a biologist at the Bird Alliance of Oregon said in a statement.
“The most common species were northern shovelers, northern pintails, and American coots, but other species are being affected as well, including songbirds and predators who are either eating the carcasses or the insects off the carcasses. It’s likely we won’t ever know the true death toll since not all birds or mammals will die in the water.”
Tule Lake National Wildlife Refuge is one of the six refuges in the Klamath Basin and plays a vital role in supporting migratory bird populations along the Pacific Flyway. The refuge is made up of shallow marshes, open water, and seasonal wetlands, which serve as critical stopover points for migratory birds during their long journeys between breeding and wintering grounds.
This region has seen outbreaks of botulism before, though these would usually only kill a few hundred birds, rather than tens of thousands. This is because the wetlands are drying up rapidly, packing greater numbers of birds into smaller areas.
The Bureau of Reclamation delivered 5,000 to 10,000 acre-feet of water to Tule Lake and Lower Klamath NWR on August 17, however, as no more water is due to be delivered this year, only rainfall and cooler weather will help end the outbreak.
“The Klamath Basin serves as a critical habitat for nesting and migrating birds along the Pacific Flyway. The devastation happening here due to the botulism outbreak will have long-lasting impacts across the entire West Coast,” Wicks said.
“The refuge and the birds can’t keep taking hit after hit, year after year. Something has to change. Without wetlands, there are no birds.”
Bird Ally X, a nonprofit organization that rescues injured birds in the region, has attempted to revive many of the affected birds, with hundreds being released back into the wild.
“I feel like we have an obligation to respond to these human-induced catastrophes,” said January Bill, Bird Ally X Co- founder/botulism co-director. “I hope the hospital’s efforts bring light to the bigger issue of the dying wetlands of the Basin. Without healthy wetlands there will be no waterbirds.”
Hunters in the wetlands are advised to avoid the area until temperatures drop.
“Avian botulism, a waterbird disease, is occurring at Tule Lake NWR impacting over 80,000 birds. Although hunting is allowed on the refuge, it is not advised until temperatures reach freezing. If you choose to hunt, please handle, clean, and cook harvested birds carefully, following the CDC guidelines for safe handling and consumption,” Klamath Basin Refuges said in a Facebook post.
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