It sounds like something from a horror movie, but it’s real. Naegleria fowleri is a tiny one-celled organism — an amoeba — that lives naturally in warm freshwater lakes, rivers, and hot springs. Most people have never heard of it. But if you’re the kind of person who jumps off docks, dives into lakes, or splashes around in slow-moving rivers during summer, this is something you genuinely need to know.
Here’s the part that surprises people: drinking water with it in it won’t hurt you. The amoeba can only infect you through your nose. When water gets forced up into your nasal passages — like when you dive in headfirst, get splashed hard, or jump in without plugging your nose — the amoeba can travel up through your nasal tissue and into your brain. Once there, it destroys brain tissue. That’s why it’s earned the nickname “brain-eating amoeba.”
Where does it like to hang out? Think warm and shallow. The Arizona Department of Health Services documented a case where a boy died after swimming and diving in Kingman Wash on the Arizona side of Lake Mead. According to data cited by Mono County, California public health officials, about 75% of infections are linked to swimming in warm freshwater lakes and rivers. But it’s not just natural water — poorly maintained swimming pools, water slides, hot tubs with low chlorine, and even neti pots used with non-sterile water have all been linked to infections in rare cases.
The infection it causes is called Primary Amebic Meningoencephalitis, or PAM. It moves fast and it’s extremely dangerous.
So what actually reduces your risk? The CDC says to hold your nose shut — or use a nose clip — any time you jump or dive into freshwater. Avoiding activities in warm, shallow water during the hottest months also helps, since the amoeba thrives when water temperatures are high and water levels are low. And if you’re using a neti pot or doing nasal rinsing for any reason, only use distilled or sterile water — never water straight from the tap.
Infections are genuinely rare. The amoeba is widespread, but it doesn’t seek out humans — it’s not a parasite with a mission. Most people swim in these waters their whole lives and never have a problem. But rare doesn’t mean impossible, and the one simple habit of pinching your nose before you hit the water costs you nothing.