Swimmer Diana Nyad has ended her fourth bid to swim from Cuba to Florida after four days of storms, jellyfish stings and shark threats.
Her support team said made the decision after being pulled from the water a day before her 63rd birthday.
Nyad left Havana on Saturday in her third attempt since last year to be the first person to swim the Florida Straits without a shark cage. She also failed once earlier to do so with a cage. This time she lasted longer, and made it further, than in her previous tries, her team said. She swam this time for more than 41 hours.
"She realised that the obstacles against this swim were too great and agreed at dawn to return to Key West by boat," a spokeswoman said.
Team member Vanessa Linsley said the swimmer encountered a triple threat of obstacles.
"Instead of getting hit with one doozy they got hit with three," she said, "They got hit with the weather, they got hit with the jellyfish and they got hit with the sharks all at the same time."
Nyad was stung nine times by box jellyfish on Monday night alone.
Overnight was the second straight night of storms encountered by the swimmer. On Monday evening, the crew was improvising ways to prevent hypothermia and to fend off further swelling of her lips and tongue.
Australian Susie Maroney successfully swam the Straits in 1997, but she used a shark cage. In June, another Australian, Penny Palfrey, made it 79 miles toward Florida without a cage before strong currents forced her to abandon the attempt.
Nyad has been training for three years for the feat. She is accompanied by a support team in boats, and a kayak-borne apparatus that helps keep sharks at bay by generating a faint electric field.