The brain-eating amoeba, Naegleria fowleri, naturally lives in warm freshwater and soil across much of the world. It thrives in lakes, rivers, ponds, hot springs, and even household plumbing, preferring water temperatures above 95°F (35°C). While infections are extremely rare, with fewer than 10 cases per year in the United States, understanding where this organism lives helps explain who’s at risk and why.
Warm Freshwater and Soil
Naegleria fowleri is not an exotic organism hiding in remote places. It’s a common inhabitant of warm freshwater environments and the sediment beneath them. Lakes, rivers, ponds, and ditches that warm up during summer months all provide suitable habitat. The amoeba also lives in soil, including the muddy bottoms of those same bodies of water, where it feeds on bacteria.
What makes a body of water hospitable comes down mostly to temperature. Naegleria fowleri is thermophilic, meaning it prefers heat. It grows in water above 95°F (35°C) and can tolerate temperatures up to about 115°F (46°C). This is why infections cluster in the warmest months of summer and in southern regions where lakes and ponds stay warm longer. Water that feels bathwater-warm is the type most likely to harbor the amoeba in significant numbers.
Saltwater is a different story. No one in the United States has ever contracted a Naegleria fowleri infection from swimming in the ocean. The amoeba does not thrive in high-salinity environments. Lab studies confirm that salt concentrations approaching seawater levels severely limit its ability to grow and reproduce.
Geothermal Water and Hot Springs
Naturally heated water sources carry particular risk because their temperatures fall squarely in the amoeba’s preferred range year-round, not just during summer. Hot springs, geothermal pools, and warm-water spas have been linked to infections in multiple countries. In one well-documented case from Costa Rica, researchers isolated Naegleria fowleri directly from a hot spring at a resort where a child had contracted a fatal infection. Samples from both the hot spring and a nearby river pond tested positive.
The constant warmth of geothermal water means the amoeba can persist there regardless of season or air temperature. If you’re swimming or soaking in a natural hot spring, the water is essentially an ideal incubator.
Household Plumbing and Tap Water
One of the less intuitive places Naegleria fowleri can live is inside your home’s water system. The amoeba can grow in public and private water tanks, pipes, and water heaters, particularly when water sits stagnant and warm. This doesn’t mean drinking tap water is dangerous. The amoeba causes infection only when contaminated water enters the nose, not the stomach.
The real household risk involves nasal rinsing. People who use neti pots, squeeze bottles, or other sinus irrigation devices with unsterilized tap water have died from Naegleria fowleri infections. At least three U.S. cases have been traced to nasal irrigation or ritual nasal washing with tap water, including two in Louisiana and one in the U.S. Virgin Islands. The CDC recommends using distilled water, previously boiled water (cooled down), or water filtered through a device with a pore size of 1 micron or smaller for any sinus rinsing.
Swimming Pools and Splash Pads
Properly chlorinated pools are safe. Naegleria fowleri cannot survive in water with adequate disinfectant levels: a minimum of 1.0 parts per million (ppm) of free chlorine, or 2.0 ppm if a stabilizer like cyanuric acid is used. The pH should stay between 7.0 and 7.8.
The danger arises when disinfection fails. In 2023, a child in Arkansas died from a Naegleria fowleri infection after playing at a splash pad where chlorine levels had not been properly maintained. These interactive water features recirculate water that can warm up in the sun, and if chemical treatment lapses, conditions become favorable for the amoeba. The key variable is not the type of water feature but whether disinfection is consistent and monitored.
Where Cases Are Most Common
Naegleria fowleri exists on every continent, but reported infections concentrate in specific regions. A global review found cases in 33 countries, with the United States accounting for 41% of all reported infections, followed by Pakistan (11%) and Mexico (9%). Between 1962 and 2024, 167 cases were reported in the U.S., the vast majority from southern states where summer water temperatures routinely exceed 95°F.
No cases have been reported from Alaska or Hawaii. The southern and central U.S. have historically carried the highest burden, with Texas, Florida, and states along the Gulf Coast reporting the most infections.
Northward Expansion
The amoeba’s range appears to be shifting. An analysis of U.S. cases has documented a northward expansion, with infections appearing in states like Minnesota, close to the Canadian border. These cases occurred in the weeks following spikes in air temperature, suggesting a direct link to warming climate patterns.
In 2023, researchers identified four Naegleria species in recreational lakes in Alberta, Canada, marking the first time the genus had been found there. While the specific species that causes human disease (Naegleria fowleri) was not among them, the presence of its close relatives indicates the environment could support its growth. As summers grow hotter and lakes in northern latitudes warm to temperatures the amoeba favors, the geographic risk zone is likely expanding.
How Infection Actually Happens
Knowing where the amoeba lives matters because of how it infects people. Naegleria fowleri enters through the nose, not through the mouth or skin. When contaminated water is forced up the nasal passages, whether from diving into a lake, jumping into a pool, or rinsing sinuses, the amoeba can penetrate the tissue lining the nose and travel along the olfactory nerves directly into the brain.
The organism has three life stages: an active feeding form (trophozoite), a temporary swimming form with whip-like tails, and a dormant cyst that can survive harsh conditions. The feeding form is what causes disease. Once it reaches brain tissue, it destroys cells as it feeds, causing a rapidly progressing infection called primary amebic meningoencephalitis. More than 97% of people who develop this infection have died from it. Of 167 U.S. cases over six decades, only four people survived.
The rarity of infection is worth emphasizing. Millions of people swim in warm freshwater every summer. Fewer than 10 get sick in the U.S. each year. But because the fatality rate is so high, avoiding forceful water entry into the nose in warm freshwater, using nose clips, and never rinsing sinuses with unsterilized tap water are straightforward precautions that eliminate the primary routes of exposure.