A dangerous amoeba that thrives in warm, freshwater bodies in the heat of summer caused the recent death of a 16-year-old Central Florida girl, the U.S. Centers for Disease Control confirmed on Monday.

Courtney Nash died Saturday, 10 days after she, her brother and four friends went swimming August 3 in the St. Johns River on Florida's east coast, her uncle, Thomas Uzel, said at a news conference.

"They were having fun just like any other kid would out in the water," he said.

The amoeba, officially known as Naegleria fowleri, is a single-cell, microscopic organism found in such freshwater bodies as lakes, rivers, hot springs and, occasionally, in neglected, unchlorinated swimming pools.

The amoeba typically enters a swimmer's nose and invades the brain causing an almost always fatal infection, according to Jonathan Yoder, an epidemiologist at the CDC in Atlanta.

Out of 118 people reported to have had the amoeba infection since 1962, only one survived, Yoder said. Most reported cases have been in the southern states of Florida and Texas, he said.

Yoder said the average age of the amoeba victims is 12. He said experts believe young people are more susceptible because they are more likely to jump into the water, dive to the bottom and otherwise play underwater in ways that force water, and potentially amoebas, up their noses.

Researchers report that the amoebas proliferate when the water temperature reaches 80 degrees Fahrenheit, but they also survive at cooler temperatures.

Anti-fungal drugs are effective against the amoeba in the laboratory, but the infection in humans typically cannot be diagnosed quickly enough to save the patient.