3 National Park Sites Test Positive for ‘Brain-Eating Amoeba’ in Water

May 6, 2026

When it comes to potential dangers in the outdoors, most people think of getting lost, slipping and falling, or encountering wildlife such as bears and mountain lions. A new study, however, shows that there’s a significant danger we can’t see with the naked eye.

Researchers recently found high concentrations of a dangerous, brain-eating amoeba in several National Park Service (NPS) managed sites in the Western U.S. The findings indicate that this microscopic parasite could be moving farther north as temperatures warm with climate change.

The study was published in ACS ES&T Water, a scientific journal devoted to research on water quality, treatment, and protection. It focused on analyzing 40 bodies of water used for outdoor recreation across five NPS-managed sites in the West: Yellowstone National Park, Grand Teton National Park, Newberry National Volcanic Monument, Olympic National Park, and Lake Mead National Recreation Area. The study analyzed 185 water samples collected from 2016 to 2024.

Scientists were looking for the presence of Naegleria fowleri, a type of amoeba that is the main cause of primary amoebic meningoencephalitis (PAM). The condition has a fatality rate of 98%. Essentially, when a person goes swimming, the amoeba can enter the brain through the nose. It then causes brain swelling and the destruction of brain tissue. Death normally occurs within 1 to 7 days of infection. Gear Junkie