'Brain-eating amoeba' surfaces in iconic US national parks. See where
Corrections and clarifications: An earlier version misstated the nature of amoebas, which are single-celled eukaryotic organisms.
A single-celled organism known as the “brain-eating amoeba” was found in two of the U.S.’s most popular national parks, according to a recently published study.
A multi-institutional study conducted between 2016 and 2024 found Naegleria fowleri, also known as the “brain-eating amoeba,” in water samples taken from three of five popular recreation areas across the western U.S.
The study, which involved researchers from the U.S. Geological Survey, Montana State University, and Commonwealth Scientific and Industrial Research Organization, was published in the American Chemical Society’s journal, ES&T Water.
Here’s what you should know about the brain-eating amoeba and where it was found in the U.S. parks and recreation system.
The scope of the study
Naegleria fowleri thrives in soil and warm freshwater lakes, rivers, ponds and hot springs all over the globe. When contaminated water enters a person’s nose, the amoeba can infect their brain with a fatality rate of 98%.
Researchers took a total of 185 samples from 40 “thermally impacted areas” across five sites − Yellowstone National Park, Grand Teton National Park, Lake Mead National Recreation Area, Olympic National Park and Newberry National Volcanic Monument − and found Naegleria fowleri in 34%, or 63, of them.
No reports of infections or deaths have been tied to the sites.
While samples from Washington’s Olympic National Park and Oregon’s Newberry National Volcanic Monument came back clean, some of the more iconic names in the study weren’t so lucky.
Yellowstone National Park
Yellowstone National Park, the country’s first official national park and the third most visited as of 2025, contains more than a few rivers and hot springs that host Naegleria fowleri. Here’s when and where it was detected:
- Boiling River: July, September and November 2018, July 2019 and September 2023.
- Firehole Canyon Swimming Area: 2018 and 2019.
- Firehole River near Goose Lake: 2023.
- Multiple hot springs at Lewis Lake: 2023.
Grand Teton National Park
Meanwhile, three hot spring areas in Wyoming’s Grand Teton National Park, the eighth-most visited park in the country last year, also tested positive. Here's when and where:
- Granite Hot Spring: 2019 in the pool above the recreational area
- Polecat Hot Springs: 2019-2024
- Huckleberry Hot Springs: 2019-2024
Lake Mead National Recreation Area
Lake Mead National Recreation Area, located just outside Las Vegas, Nevada, also proved to be a hotbed for Naegleria fowleri activity.
Between 2018 and 2019, four of its five sample sites, all of which were hot springs, tested positive, including Blue Point, Boy Scout, Nevada and Roger’s.
The scope of the problem
According to the Centers for Disease Control and Prevention, fewer than 10 people in the U.S. die each year from primary amebic meningoencephalitis, or PAM, the infection caused by Naegleria fowleri. However, of the 167 reported cases of PAM between 1962 and 2024, only four people survived.
Infections typically occur when contaminated water enters the nose and travels up the nasal passages into the brain, often when people are diving, swimming, or simply relaxing in rivers, lakes, and hot springs.
Early symptoms include headache, fever and nausea, before progressing to confusion, coma and seizures. Death ultimately occurs 7 to 10 days after a person is infected.
The researchers note in their study that the amoeba has been steadily migrating northward since 1962, a phenomenon that’s expected to continue as global temperatures rise. As such, they’re advocating for better monitoring systems and risk management strategies, as well as a robust public awareness campaign.
This story has been updated to correct a factual error.
Drew Pittock covers national trending news for USA TODAY. He can be reached at [email protected].