Swimmers often welcome the warm temperatures of summer, particularly when the intense sunlight warms water in their favorite lakes and ponds. However, there is a rare but serious threat lurking in some of these pleasant waters. The recent death of a nine-year-old Kansas girl serves as a grim reminder.

The potentially deadly agent in some warm water bodies is an amoeba that once in the brain, destroys neurons by feeding on them. The single-celled organism Naegleria fowleri, a kind of amoeba, thrives in water that warms into the 70 to 80 degree Fahrenheit range. According to the U.S. Centers for Disease Control and Prevention (CDC), the amoeba may be present in fresh water lakes, ponds, rivers, hot springs, untreated swimming pools, and even home hot water heaters. Even tap water that has not been sufficiently treated with chlorine may potentially harbor the nasty agents.

Some experts link the risk of amoeba exposure to climate change. Dr. Clayton Wiley at the University of Pittsburgh Medical Center’s division of neuropathology hypothesizes that an overall warming of summer temperatures may translate into more bodies of water containing more of these microscopic creatures.

The risk of infection is extremely rare, but cases are nearly always lethal. Among approximately 132 suspected or documented cases since 1962, only three have survived, according to the CDC. Last year, 13-year-old Kali Hardig of Benton, Arkansas, survived an infection she contracted while swimming in a local water park. Her symptoms were fever and severe headache.

“I took her temperature and it was 103.6,” mother Traci Hardig said in a telephone interview. “I couldn’t get it to go down and it kept going up. She wouldn’t drink anything and then she started projectile vomiting. Her eyes rolled back in her head and I said, ‘Oh my God, there is something really wrong with this baby.’”

The amoeba needs to enter the body through the nasal passages so water-goers are advised to keep water out of their noses and flush their sinuses well after a suspected exposure.