Havana, Cuba (CNN) -- A jellyfish sting has stopped an Australian endurance swimmer, just 11 hours into her attempt to swim from Cuba to Florida.
Chloe McCardel was forced to end her journey prematurely "due to a severe debilitating jellyfish sting," a spokesman said in a statement.
The swimmer was on a boat heading toward Key West on Wednesday night, spokesman Tim Stackpool said.
"She will spend the next 24 hours recuperating before deciding on her plans going forward," he said.
Earlier Wednesday, McCardel -- slathered in a thick coat of sunscreen -- lept into the waters off Havana to begin her daunting 100-mile swim across the Florida Straits.
Her goal was to set a world record for the longest unassisted swim. Before diving in, McCardel said she expected her marathon swim through shark- and jellyfish-infested waters to take 60 hours.
"I think it will all work out well," said McCardel, 28. "It will be tough though; it's not going to be an easy ride. But we will get through it as a team."
The attempt cost around $150,000 to finance, McCardel said earlier. She said she hoped to raise money for cancer research and try to improve U.S.-Cuba relations.
Each stroke the Australian swimmer took was monitored by teammates in two boats escorting her and by scientists at three universities in the United States.
But other than liquid meals handed to her in a bottle every half-hour by a kayacker paddling near her, McCardel said she would not receive help during the long-distance swim and not use any swim aids such as flippers or a wet suit.
In 1997, fellow Australian Susie Maroney swam the straits from inside a shark cage.
Since then, several high-profile attempts to cross the Florida Straits without a shark cage have been attempted. All have failed.
McCardel said she would use "a shark shield" device that emits an electromagnetic pulse to keep away hungry predators. But forgoing a full body suit made her more exposed to jellyfish stings.
CNN's Catherine E. Shoichet contributed to this report.