Scientists Confirm ‘Brain-Eating Amoeba’ Is Widespread In Yellowstone And Grand Teton

Brain-eating amoebas are thriving in Yellowstone and Grand Teton National Parks, and they are probably more widespread than most people realize, new research confirms. Scientists detected Naegleria fowleri—the cause of a fast-acting brain infection with an average mortality rate of 97%—in several spots including Yellowstone’s Boiling River and Grand Teton’s Huckleberry and Polecat Hot Springs. Infections are extremely rare, and there is no known cure.

“Just keep your head above water,” said Elliott Barnhart, a microbiologist with the U.S. Geological Survey and co-author of the new paper. “Infections are very rare, but it’s important to learn as much as we can about these systems so people can stay safe.”

The presence of Naegleria fowleri in northwest Wyoming is not a new discovery. It was first confirmed in Yellowstone in the early 2000s. The new study, which collected and analyzed 185 water samples from Yellowstone, Grand Teton, and Fort Meade National Recreation Area in South Dakota, found “widespread detections” in 34% of samples. Brent Payton, a professor at Montana State University and another contributor, said the study was the most extensive sampling in terms of years and locations. “We’re not the first to show that it’s present in the parks,” he said. “We’ve known that for 20 years.”

When in water, Naegleria fowleri is inert and harmless to humans. But when it enters the body through the nose, it feeds on nerve tissue, causing extensive brain and central nervous system damage. According to a 2025 study, 488 cases of primary amoebic meningoencephalitis (PAM) have been reported worldwide since 1962, with 167 cases in the United States. Only seven people survived. Last year, a 71-year-old Texas woman died after using a sinus rinse with contaminated water as part of a religious ritual.

“The only exposure route we’re aware of is through the nose,” Barnhart said. “As long as you keep your head above water and don’t stick moss or seaweed up your nose, the chances of exposure are very low.”

The researchers emphasized that the study’s findings do not necessarily mean the amoeba is spreading. Rather, enhanced DNA testing has made it easier to detect. Barnhart said it is entirely possible that the amoeba is much more widespread in both parks; it just has not been detected yet. “There are a lot of places where nobody’s ever looked for it,” Payton said.

Most Yellowstone and Grand Teton visitors will not risk exposure because soaking in hot springs is strictly prohibited, and spots where people used to swim, like Boiling River, are indefinitely closed. People keen to swim need only wear a nose clip. Barnhart noted that the research team kept encountering the same people soaking at hot springs where they confirmed widespread Naegleria concentrations. “They were educated about keeping their head above water,” he said. “That’s our goal—to increase awareness.”

Payton said he still goes swimming in hot springs every chance he gets. “PAM is extremely rare but obviously devastating if it happens,” he said. “If you do these simple things, you can avoid it.”