Brain-eating amoeba detected in western national park waters

May 7-A new federal study has found a rare but dangerous "brain-eating amoeba" in warm recreational waters at several western national park sites - including the Lake Mead National Recreation Area, Yellowstone National Park and Grand Teton National Park.

Researchers detected Naegleria fowleri, a microscopic amoeba that causes a typically fatal brain infection, in water samples collected from thermally influenced recreation sites across the West, such as hot springs, geothermal systems and shallow warm-water areas. The study, published by the U.S. Geological Survey and its partner agencies, tested 185 water samples from 40 sites and detected the amoeba in about one-third of all samples collected.

The organism is commonly called the "brain-eating amoeba" because it can cause an infection known as primary amebic meningoencephalitis, or PAM. Infection occurs when contaminated water enters through the nose - usually while swimming, diving or participating in water sports in warm freshwater. Infections are extremely rare, but the disease has a fatality rate of 98%, according to the study.

The Centers for Disease Control and Prevention wrote that the U.S. saw 167 reported cases of PAM between 1962 and 2024 - and just four people survived it.

"These findings indicate that N. fowleri is present in thermally impacted areas across the western United States and underscore the use of enhanced monitoring, public awareness, and risk management strategies in thermally influenced recreational waters," the authors of the study wrote.

The findings are likely to draw particular attention at Lake Mead, where a child died in 2022 after being exposed to the amoeba at the reservoir near Las Vegas. Following the death, officials warned visitors to avoid getting warm freshwater up their noses, especially while diving or participating in water sports during the hottest parts of the summer.

Researchers said warming temperatures may help expand the range of Naegleria fowleri, which thrives in warm freshwater environments. The amoeba is typically found in water temperatures above 86 degrees Fahrenheit and can multiply rapidly during periods of extreme heat.

"Cases of PAM in the United States (U.S.) have seen a northerly geographical expansion since 1962, and the trend is predicted to continue as global temperatures increase," the authors of the study wrote.

Many of the sites tested were remote geothermal areas or low-use thermal waters rather than heavily trafficked swimming beaches or major recreation hubs, though researchers noted that the findings still highlight the need for awareness in warm freshwater environments.

Editor's note: This story was updated at 12:30 p.m., May 7, to correct the national park sites where Naegleria fowleri was detected.

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This story was originally published May 6, 2026 at 7:21 PM.