NorCal Lake Sees its Worst Botulism Outbreak in History, Killing More Than 75,000 Birds

The Tule Lake National Wildlife Refuge in the Klamath Basin, near the California-Oregon border, is facing its worst botulism outbreak in history, with an estimated 75,000 to 80,000 birds dead and thousands more expected to perish in the coming weeks.

Samples from the lake tested positive for avian botulism on August 23, confirmed by the USDA’s National Veterinary Services Laboratory. The disease, caused by toxins from the Clostridium botulinum bacteria, affects primarily waterfowl and shorebirds, leading to paralysis, respiratory failure, or drowning.

Teresa Wicks, a biologist with the Bird Alliance of Oregon, reported seeing around 500 dead birds, including northern shovelers, pintails, and American coots. “It’s likely we won’t ever know the true death toll since not all birds or mammals will die in the water,” Wicks said.

Tule Lake National Wildlife Refuge, one of six refuges in the Klamath Basin, is a vital stopover for migratory birds on the Pacific Flyway. However, with rapidly drying wetlands, birds are now concentrated in smaller areas, intensifying the impact of the outbreak.

The Bureau of Reclamation delivered some water to the refuge in August, but no additional water is expected this year, leaving cooler weather and rain as the only hopes to end the outbreak. Wicks expressed concern about the long-term impacts, stating, “Without wetlands, there are no birds.”

Hunters 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,” Klamath Basin Refuge said on social media. “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.”