May 29, 2008 -- Six young men died last year after swimming in lakes or pools infested with a brain-eating amoeba, the CDC reports.

The bad blobs -- known as Naegleria fowleri or N. fowleri -- thrive in warm, fresh water all over the world. But the key word here is warm. The amoeba loves heat. In the U.S., it inhabits the relatively hot waters of lakes, hot springs, and poorly maintained pools in Southern or Southwestern states.

All six of the 2007 cases were in Florida, Texas, and Arizona (the victims' names and swimming sites come from local media reports):

May/June 2007: Angel Arroyo Vasquez, age 14, of Orlando, Fla., was swimming in an apartment swimming pool.

July 2007: Will Sellars, age 11, of Orlando, Fla., was swimming and wakeboarding in Lake Conway.

August 2007: Richard Almeida, age 10, of Kissimmee, Fla., was swimming and wakeboarding at Orlando Watersports Complex.

August 2007: John "Jack" Herrera, age 12, participated in water activities during summer camp at Lake LBJ in Texas.

August 2007: Colby Sawyer, age 22, ruptured his eardrum while wakeboarding at Lake LBJ in Texas.

September 2007: Aaron Evans, age 14, was swimming at Lake Havasu in northeastern Arizona.

Why the deadly amoeba struck these six and not the thousands of other people exposed in the same places at the same times is a mystery, says CDC epidemiologist Jonathan Yoder.

"Humans are the accidental host -- we are not part of this amoeba's life cycle," Yoder tells WebMD. "But when it finds a nice warm environment like your nose, it looks for a food source."