Naegleria fowleri thrives in warm, standing freshwater and the sediment of rivers and lakes. And while it's usually harmless, it can cause fatal brain swelling if inhaled through the nose.
Early symptoms of a Naegleria infection include a severe frontal headache, fever, nausea and vomiting, according to the CDC. But those can swiftly give way to a stiff neck, seizures, confusion and hallucinations as the amoeba makes its way up through the nasal cavity into the brain.
"After the start of symptoms, the disease progresses rapidly and usually causes death within about five days," the CDC's website reads. "People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck and vomiting, particularly if they have been in warm freshwater recently."
ABC News' Katie Moisse contributed to this report.