Updated May 6, 2026 12:26PM<\/p>\n<\/div>\n
Some of the country\u2019s most popular national parks are hiding a potentially deadly secret in their water. As part of a new study<\/a>, researchers found Naegleria fowleri <\/em>(N. fowleri<\/em>), also known as the \u201cbrain-eating amoeba<\/a>,\u201d in hot springs and hydrothermally fed waters across Lake Mead Recreation Area, as well as Grand Teton and Yellowstone National Parks.<\/p>\n Though rare, the pathogen kills 98 percent of those infected within five to ten days.<\/p>\n As part of the study, researchers at the U.S. Geological Survey and Montana State University analyzed 40 recreational waterways across five western National Park Service (NPS) sites, including Yellowstone, Grand Teton, and Lake Mead Recreation Area. They detected the amoeba in 34 percent of samples.<\/p>\n \u201cPeople can become infected when they go swimming or diving in contaminated warm fresh water,\u201d wrote the NPS on its website<\/a>. \u201cInfection occurs when the organism enters the body through the nose and travels to the brain, causing Primary Amebic Meningoencephalitis (PAM), which is almost always fatal.\u201d\u00a0<\/strong><\/p>\n As much of the United States faces drought conditions, experts warn that cases of the deadly pathogen could increase as temperatures rise. The amoeba thrives in warm pools up to 115 degrees Fahrenheit, and water across western national parks is\u00a0getting warmer<\/a>.<\/p>\n Brent Peyton, one of the study\u2019s authors, told Outside\u00a0<\/em>that the findings aren\u2019t surprising as the pathogen is found worldwide. What was unexpected, however, was its high concentration at some sites.<\/p>\n \u201cSome of the sites we sampled had N. fowleri<\/em> concentrations greater than other sites with a known fatality,\u201d Peyton said.<\/p>\n Cases of amoeba infection have expanded northward since 1962 as temperatures have steadily increased nationwide. The pathogen lives in soil, warm freshwater lakes, rivers, ponds, and hot springs. More specifically, it thrives in waters between 71 and 86 degrees Fahrenheit, including many of the nation\u2019s most cherished backcountry hot springs. As more than half of the country<\/a> is currently experiencing drought, experts warn<\/a> cases of infection could continue to rise.<\/p>\n \u201cN. fowleri<\/em> is very widespread and found in many recreational waters, not just national park hot springs,\u201d Peyton said. \u201cInfections are very rare, but we believe we are seeing the geographic range of cases spread over time, perhaps due to climate change.\u201d<\/p>\n Between 1962 and 2024, the Centers for Disease Control and Prevention (CDC)\u00a0reports<\/a> that\u00a0there were 167 infections in the U.S. Only four people with the infection have survived. Although the CDC says fewer than ten people become infected annually, other estimates<\/a> suggest as many as 16 deaths occur in the U.S. on average every year, as a result of this fatal pathogen.<\/p>\n \u201cThese findings indicate that N. fowleri<\/em> 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,\u201d the researchers wrote<\/a> in the study.<\/p>\n As part of the study, researchers at the U.S. Geological Survey and Montana State University analyzed 40 recreational waterways across five western National Park Service (NPS) sites, including Yellowstone, Grand Teton, and Olympic national parks, as well as Newberry National Volcanic Monument in Oregon and Leake Mead Recreation Area. They detected the amoeba in 34 percent of samples\u2014but none in Newberry or Olympic.<\/p>\n Polecate Hot Springs, accessed by a popular 2.5-mile trail in Grand Teton, contained the highest concentration of N. fowleri<\/em> at levels that can exceed public health limits. Both upper and lower pools tested positive. Researchers also detected the amoeba in Grand Teton\u2019s Huckleberry and Granite Hot Springs.<\/p>\n In Yellowstone National Park, researchers found the amoeba in the Boiling River, where hydrothermal water mixes with the river. Researchers also detected the amoeba at Lewis Lake, specifically at multiple springs on the southern shore, and the Firehole River\u2019s Goose Lake and Firehole Canyon Swimming Area.<\/p>\n Four sites in Lake Mead Recreational Area tested positive for the pathogen, including Boy Scout, Nevada, Blue Point, and Roger\u2019s Hot Springs.<\/p>\n The NPS warns that postage signage is typically not used at park sites to label areas where the pathogen is present. Rather, people should assume that it \u201ccan be present in warm freshwater bodies across the United States.\u201d<\/p>\nThe Pathogen is Migrating North as Temperatures Warm<\/h2>\n
Brain-Eating Amoeba Detected in Popular Hot Springs<\/h2>\n