Nyad, seeking to become the first person to swim the 103 miles from Cuba to the United States without a shark cage, was taken from the water Monday night when a storm hit, a posting on her Web site said.
Nyad, who turned 63 Wednesday, reportedly told crew members she wanted to get back in the water but the storm, punctuated by lightning and "roiling winds," led her and the crew to stop the attempt.
"She realized the obstacles against this swim were too great and agreed at dawn to return to Key West by boat, for the sake of the safety of her team and herself," the posting said.
In addition to the weather, Nyad was threatened by jellyfish and sharks. Photographs on the Web site showed the swimmer's face swollen because of jellyfish stings and teams of divers worked to keep sharks at a safe distance. The Web site report said Nyad was stung nine times Monday night by jellyfish
Her swim began Saturday and ended after Nyad had been in the water for nearly 42 hours. The Web site said she swam farther than in each of her previous attempts of swimming from Cuba to the United States.
Her try last year ended after 41 hours in the water after she was stung by jellyfish.
Nyad once swam around the island of Manhattan (1975) and 102 miles from the Bahamas to Florida (1979).