Brain-Eating Amoeba Detected in U.S. National Parks: What You Need to Know

Yes, you read that right: Naegleria fowleri, commonly known as the "brain-eating amoeba," has been detected in two popular U.S. national parks, according to a recent study published in the American Chemical Society’s journal, ES&T Water.

The study, conducted by the U.S. Geological Survey and other institutions, analyzed 185 water samples from five national parks over an eight-year period (2016–2024). The parks included:

• Yellowstone National Park
• Grand Teton National Park
• Lake Mead National Recreation Area
• Olympic National Park
• Newberry National Volcanic Monument

The researchers examined 40 thermally impacted recreational waters, including hot springs. Their findings revealed that 34% of the samples (63 specimens) tested positive for Naegleria fowleri in Yellowstone, Lake Mead, and Grand Teton. Notably, the amoeba was not detected in samples from Olympic National Park or Newberry National Volcanic Monument.

Crucially, no infections or deaths have been reported at these sites due to the amoeba.

What Is Naegleria fowleri?

Naegleria fowleri is a free-living, single-celled organism that thrives in warm freshwater, including lakes, rivers, and hot springs. It earned the nickname "brain-eating amoeba" because it can infect and destroy brain tissue, according to the Centers for Disease Control and Prevention (CDC).

While infections caused by Naegleria fowleri are rare, they are nearly always fatal. The CDC reports a 98% fatality rate for infections. If water containing the amoeba enters the nose and reaches the brain, it can cause primary amebic meningoencephalitis (PAM).

In the U.S., fewer than 10 people per year contract PAM. However, only four survivors have been reported out of 167 cases between 1962 and 2024.

Exposure Risks

Infections typically occur after swimming or diving in freshwater during hot summer months, when water temperatures rise and levels drop. The CDC emphasizes that swallowing water with the amoeba does not cause infection, nor can it spread from person to person.

How to Reduce Your Risk

The CDC recommends the following precautions to minimize exposure:

• Hold your nose or wear a nose clip when jumping or diving into freshwater.
• Keep your head above water in hot springs.
• Avoid digging in shallow water, as the amoeba is more likely to be present in these areas.

Signs and Symptoms of PAM

Symptoms of a Naegleria fowleri infection progress rapidly and may include:

• Headache
• Fever
• Nausea and vomiting
• Stiff neck
• Confusion or lack of attention
• Loss of balance
• Hallucinations

According to the CDC, most people with PAM die within 18 days of initial symptoms, with many entering a coma and dying within 5 days.