FAQs: Botulism Outbreak Management

What is the status of the botulism outbreak?

The first botulism-affected bird was found on June 27, 2026. Since that date, mortality numbers have slowly risen, and botulism is now affecting birds in both wetland 1A and 1B at Tule Lake National Wildlife Refuge. Refuge staff estimate total mortality is at least 13,730 birds as of August 18. Wetland 1A is experiencing the highest daily mortalities while wetland 1B is experiencing more widespread mortality throughout the wetland.

What actions are being taken to mitigate the outbreak?

Refuge staff are collecting carcasses to prevent the spread of botulism and working with partners in the watershed community to explore changing water levels in the refuge to increase wetland elevation and reduce toxin concentration.

The U.S. Fish and Wildlife Service is also exploring the option of scaling up operations at the refuge’s duck hospital to rehabilitate infected birds, as we have during previous botulism events. We will continue to work with partners across the watershed to improve water management that benefits the holistic ecosystem function to support fish, wildlife, wetlands, farms and recreation.

What causes avian botulism?

Avian botulism is caused by a naturally occurring bacterium in the soil that produces a paralytic toxin and accumulates in the food waterbirds forage on. Botulism spores germinate in soil exposed by falling water levels during hot summer days. A botulism outbreak typically begins when birds consume toxin-carrying invertebrates and then quickly moves into a cycle involving fly maggots.

Fly maggots contain a higher concentration of the toxin, resulting in more carcasses facilitating exponential growth of the mortality event. Death in avian species generally occurs within 24 hours of toxin ingestion and is often the result of drowning due to paralysis from the toxin. Botulism will remain active in the wetland system until the fly cycle is stopped by a prolonged freezing event, though additional water added to the system can mitigate the impacts of botulism ahead of the eventual freeze.

Is there a threat to pets or humans?

We are facing botulism caused by Clostridium botulinum type C, which poses low risk to humans and pets. It's best to keep pets away from water where botulism is present. Please continue to monitor our website and the refuge’s Facebook page to stay informed about potential safety risks.

Will the toxin spread to nearby refuges or agricultural fields?

There is currently no risk of the toxin spreading to other refuges or nearby agricultural fields. Botulism is a naturally occurring bacteria in many wetland systems and is already present in soils at Lower Klamath National Wildlife Refuge.

What species are being impacted by the outbreak?

The ongoing botulism outbreak has mostly affected waterfowl species. Waterbirds, including white-faced ibis and several grebe species, have been impacted as well. Additionally, a few muskrats have also been affected. We are not aware of any impacts to fish species.

How many birds used the Lower Klamath and Tule Lake National Wildlife Refuges this year?

Lower Klamath and Tule Lake National Wildlife Refuges reported an estimated 80,000 to 100,000 waterbirds hatched this year, accompanied by approximately 200,000 to 300,000 molting adults. These figures represent the highest recorded numbers of breeding season waterbirds in recent decades.

How does this year’s outbreak compare to previous years?

This year’s botulism outbreak began earlier in the year compared to recent years. Due to the earlier onset, it has affected a greater number of young birds hatched this year in comparison to previous events. As of August 18, refuge staff estimate total mortality for the 2026 botulism outbreak is at least 13,730 birds, 30 to 40 percent of which are birds hatched this year.

For context, the official final count of deceased birds due to botulism during the 2025 outbreak is at least 3,400, including 5 to 10 percent of that total being birds hatched that year. The official final count of deceased birds due to botulism during the 2024 outbreak is at least 128,000, including 5 to 10 percent of that total being birds hatched that year.

Due to several factors, we cannot say with certainty how many birds have died because of botulism.

What can the public do to help?

At this point, we are not seeking volunteers to assist with bird collection. Please continue to monitor our website and the refuge’s Facebook page to stay informed about potential safety risks.