Sixty-one-year-old American swimmer Diana Nyad was forced to end her bid to become the first person to swim from Cuba to Florida without a shark cage in mid-trip on Tuesday, CNN reported.
CNN, which had a producer on one of the boats accompanying Nyad, said she was vomiting when she was brought aboard a boat at 12:45 a.m. (0445 GMT).
She was about 29 hours into a swim that had been expected to last about 60 hours, with Key West in the Florida Keys her intended destination.
"I am not sad. It was absolutely the right call," CNN quoted her as saying.
Nyad was shielded by an electrical field to ward off sharks in her bid to set a world record by completing the 103-mile (166 km) crossing from Cuba without a shark cage.
CNN producer Matt Sloane, on one of the accompanying boats, had reported on Monday in a Tweet that the swimmer was experiencing some pain in her shoulder and "a little touch of asthma" but was otherwise moving strongly more than 18 hours into her swim.
Nyad had plunged into the warm sea at the Marina Hemingway on the western outskirts of the Cuban capital Havana at 7:45 p.m. (2345 GMT) on Sunday, cheered on by well-wishers.
Her little flotilla of escort vessels included specially equipped kayaks transmitting an anti-shark shield in the form of an electronic signal that is annoying to the sleek ocean predators that stalk the waters of the Florida Straits.
Nyad, who was raised in south Florida and turns 62 later this month, had tried the crossing from Cuba in 1978 at the age of 28, but failed in the face of winds and heavy waves.
The same swim was completed successfully in May 1997 by Australian Susan Maroney, who was 22 at the time. But Maroney used a shark cage.
"I don't want to have that asterisk at the end of my name at the end of this. I want this to be 'that was the first swim ever done without a shark cage, from Cuba to Florida,' just point blank," Nyad told MSNBC's Today Show."