Brain-eating amoeba found in hot springs at 3 National Parks: study
A new study detected Naegleria fowleri, better known as "brain-eating amoeba" in thermal waters at Yellowstone, Grand Teton and Lake Mead.
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A rare “brain-eating amoeba” was detected in hot springs and thermally influenced waters at three popular national parks in the West, according to a recent study.
Researchers found Naegleria fowleri in samples from Yellowstone National Park, Grand Teton National Park and Lake Mead National Recreation Area. The amoeba can cause primary amoebic meningoencephalitis, or PAM, a rare brain infection that can be fatal.
The study, published in ACS ES&T Water, analyzed 185 water samples from 40 thermally impacted recreational waters between 2016 and 2024. Overall, 34% of the samples tested positive for N. fowleri. Samples were collected at Yellowstone, Grand Teton, Olympic National Park, Newberry National Volcanic Monument and Lake Mead. The amoeba was not detected in samples from Olympic or Newberry; however, other nonpathogenic Naegleria species were found there.
Where brain-eating amoeba was found in national parks
File photo: Firehole River at Yellowstone National Park. NPS / Jacob W. Frank
Researchers detected N. fowleri in Yellowstone’s Firehole River, Boiling River and Lewis Lake hot spring areas. Positive detections were also reported in the greater Grand Teton region, including Polecat and Huckleberry hot springs.
According to the National Park Service, there are only a few places in Yellowstone where swimming is allowed. Swimming and soaking is prohibited in geothermal features at Yellowstone. Currently, swimming is closed at Boiling River because of impacts from the 2022 floods. The Firehole River swim area is open seasonally.
Around Lake Mead, the amoeba was found in Blue Point, Boy Scout, Nevada, and Rogers hot springs.
Measured concentrations ranged from 4.9 to 115.7 cells per liter in quantified samples. The highest concentration was recorded at Polecat Hot Spring in the Grand Teton region in September 2023. Researchers said some concentrations in Yellowstone and Grand Teton were higher than levels previously linked to PAM infections.
How amoeba infection happens
File photo: The Rogers Spring foot bridge at Lake Mead Recreation Area. (Image: NPS)
The amoeba does not infect people when contaminated water is swallowed. Infection can occur when warm freshwater containing N. fowleri enters the nose, allowing the amoeba to travel to the brain.
Most U.S. cases have been linked to swimming, diving or other water activities in warm freshwater. Fewer than 10 cases are typically reported in the United States each year, according to the Centers for Disease Control and Prevention.
Symptoms can include headache, fever and nausea before worsening to confusion, seizures and coma. The infection often progresses quickly and can be fatal within days.
How to lower the risk
Health officials say the best way to reduce risk is to keep warm freshwater out of the nose. The CDC recommends avoiding putting the head under water in hot springs and other warm freshwater, holding the nose shut or using nose clips during water activities, and avoiding stirring up sediment in shallow, warm freshwater areas.
The study’s authors said the findings highlight the need for public awareness and continued monitoring as warm freshwater recreation increases and temperatures rise.
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