Two days after a man died after going down a popular water slide, Hall County investigators have not determined how the 21-year-old died.

Monday evening, lifeguards pulled Sergio Edwards, who was unresponsive, from the water beneath the Fun Dunker at Lake Lanier Islands, Grier Todd, CEO for the water park, told the AJC. Lifeguards began administering CPR before Hall County emergency responders arrived, Todd said.

Edwards, of Illinois, was transported to Northeast Georgia Medical Center, where he was pronounced dead early Tuesday. The cause of death has not yet been determined, a spokeswoman for Hall County Coroner Marion Merck told the AJC Wednesday afternoon.

The slide, which has been at the park since 1998, is functioning properly, leaving officials at the resort puzzled over what caused the accident, Todd said.

"There's never been anything like this at the water park," Todd said. "Lake Lanier Islands extends its deepest sympathy to the family."

Edwards was a 2008 graduate of Thornridge High School in Dolton, Ill., located about 20 miles south of Chicago, former classmate Keionna Thompson told the AJC.

"Sergio was a very popular guy and was very well known for his athleticism," Thompson said.

That athleticism led Edwards to karate when he was 9 years old, John Venson, director of Just for Kicks in Chicago, told the AJC. Edwards was an instructor at the school and also competed, Venson said.

"Sergio was one of our young, outstanding instructors," Venson told the AJC. "He not only was an outstanding athlete, he was an honor student at school. He had such a promising future."

Venson said Edwards, who was visiting Atlanta when he died, was a good swimmer who had previously been to the Lake Lanier water park. Venson said he believes his friend may have hit his head on the way down, knocking him unconscious.

Edwards was scheduled to teach a class Saturday and compete in a karate event Sunday in Chicago, Venson said.

Edwards' death was one of several on metro Atlanta waters over the holiday weekend. Six people drowned in separate incidents on Lake Lanier, Lake Allatoona and a Clayton County reservoir.