When temperatures soar and a refreshing dip in the water seems irresistible, you may naturally gravitate to a freshwater lake or river if you're not near the ocean. What many people don't realize is that these seemingly idyllic swimming holes can carry a very rare yet gravely serious risk: infection by the "brain-eating" amoeba, Naegleria fowleri.
Originally discovered in South Australia during the 1950s, Naegleria fowleri can cause a dangerous condition known as primary amoebic meningoencephalitis. Although extremely uncommon, the infection is often fatal -- data from the United States show that of 164 reported cases from 1962 to 2023, only four people survived. Children and young adults (particularly young males) are most affected, with an average age of 12.
This single-celled organism thrives in fresh, warm water between roughly 25°C and 40°C. It cannot live in saltwater or chlorine-treated water, which is why well-maintained swimming pools and municipal water supplies are safe. Infections happen when water containing the amoeba enters the nasal passages -- not through drinking. Once inside the nasal tissues, the amoeba can travel to the brain, producing flu-like symptoms that can escalate quickly. Although survival odds are slim, immediate medical treatment is crucial. You can lower the risk further by choosing clean, chlorinated pools or by avoiding head submersion in warm, stagnant freshwaters that might harbor the amoeba.