Safety
Naegleria fowleri and Hot Springs: The Real Risk Explained
Last updated October 22, 2026 · 2 min read
Naegleria fowleri is a single-celled organism that lives in warm fresh water and soil. It is often called the brain-eating amoeba because, in very rare cases, it causes primary amebic meningoencephalitis (PAM), a brain infection that is almost always fatal.
How infection happens
The amoeba enters through the nose, usually when someone dives, jumps or puts their head under warm fresh water. It travels to the brain along the olfactory nerve. You cannot get it by swallowing water, and it does not spread from person to person.
Why it matters at hot springs
The amoeba thrives in water around 80°F to 115°F (27°C to 46°C), which matches many natural hot springs. Cases have been linked to geothermal water in the US and in New Zealand, where signs at natural pools warn visitors to keep their heads above water.
How rare it is
The CDC reports fewer than 200 cases in the US since 1962. Millions of people swim in warm fresh water every year. The risk is very small, but because the infection is so serious, simple precautions are worth taking.
How to protect yourself
- Keep your head above water at natural hot springs.
- Do not dive, jump or dunk.
- Use a nose clip if you might get water up your nose.
- Do not stir up sediment, where the amoeba can live.
- Choose treated pools if you want to swim underwater.
Symptoms to know
Early symptoms, usually starting one to twelve days after exposure, include severe headache, fever, nausea and vomiting, followed by stiff neck and confusion. Anyone who develops these after warm freshwater exposure should seek emergency care and mention the exposure.
Read our full hot spring safety guide.
Frequently asked questions
How common is Naegleria fowleri infection?
Very rare. The CDC reports fewer than 200 US cases since 1962, typically zero to eight a year, but almost all were fatal.
Can you get Naegleria fowleri from drinking hot spring water?
No. Infection happens only when contaminated water goes up the nose. Swallowing the water does not cause this infection.
Do hot springs test for Naegleria fowleri?
Developed pools that use chlorine or other treatment and flushing are much lower risk. Natural pools are not tested, so the safest approach is to keep your head above water.