This Lake Just Saw Its Worst Botulism Outbreak

California's Tule Lake has seen its fair share of disasters in recent years. In 2020, a botulism outbreak at the national wildlife refuge killed an estimated 60,000 birds. The following year, birds vanished as the lake, which has existed for hundreds of thousands of years, dried up for the first time in recorded history. The birds returned as the government released water into the lake last October, but hundreds died of bird flu earlier this year. Now, officials say more than 94,000 have died in the worst botulism outbreak ever recorded at the site, per the Guardian. The bacterial illness paralyzes birds of all kinds, leaving them to suffocate or drown.

It stems from Clostridium botulinum, a naturally occurring toxin that thrives in Tule's shallow, stagnant waters. Historically filled by winter rains, the lake is now supplied almost exclusively by irrigation canals. It's one of a limited number of wetlands available to the millions of birds that migrate along the Pacific Flyway. "In the Klamath Basin alone, more than 90% of wetlands have been lost," the Bird Alliance of Oregon explained last month, per KPTV. "As wetlands continue to shrink and dry up across the Intermountain West, birds are forced into smaller bodies of water," creating the kind of congestion in which botulism easily spreads.

"Combined with longer warm, dry periods in summer and early fall, this creates perfect conditions for massive, non-natural outbreaks," said the alliance. The Guardian reports the death toll from the outbreak is "almost certain to surpass 100,000." However, Bird Alliance biologist Teresa Wicks noted, per the release: "It's likely we won't ever know the true death toll, since not all birds or mammals will die in the water." Ducks Unlimited notes the number of birds using the Pacific Flyway is down 25% this year compared with last. Experts say better water flow and a restoration of wetlands will be needed to prevent a similar outbreak in the future. "Without wetlands, there are no birds," said Wicks. (More birds stories.)