(CNN) -- Hindered by painful stings and strong currents, endurance swimmer Diana Nyad ended her latest attempt to swim from Cuba to Florida about two-thirds of the way through the crossing Sunday.
The 62-year-old Nyad suffered jellyfish and Portuguese man-of-war stings Saturday, while ocean cross-currents were pushing her off course, team captain Mark Sollinger said. She was pulled out of the water about 11 a.m. Sunday, about 67 nautical miles through the 103-nautical-mile passage.
Treading water before being helped out of the water, Nyad said the man-of-war stings had paralyzed some of the muscles in her back, given her chills and nausea. Doctors warned her she could suffer long-term health problems if she suffered another sting.
"I've never been in any pain, ever, like that in my whole life," she said, adding, "Now it's set me so far back, I just don't' have the lung capacity to swim the way I can."
It was her third attempt to make the swim from Cuba to Florida. Her first, in 1978, was brought to an end by strong currents and bad weather after almost 42 hours in the water.
She made a second try in August, before she was pulled from the water after 60 miles and almost 29 hours of swimming. She blamed a shoulder injury she suffered early in the journey, and an 11-hour-long asthma attack.
Her latest attempt, accompanied by shark divers, began just after 6 p.m. Friday from Havana's Hemingway Marina. The former world champion swimmer projected the swim would take close to 60 hours.
There was a bit of excitement early Saturday afternoon as an oceanic whitetip shark swam near Nyad, but a diver on her team faced it off and it meandered away.
The swimmer improved her performance late Saturday morning after struggling to maintain her usual stroke rate, her support team said. Fortified by chicken soup, Nyad was making good progress until the Saturday evening incident.
Nyad got back in the water at 12:20 a.m. Sunday and swam for nearly 11 hours before packing it in.
"But for each of us, isn't life about determining your own finish line?" she said in a statement on her website. "This journey has always been about reaching your own other shore no matter what it is, and that dream continues."
CNN's Matt Sloane and Shasta Darlington contributed to this report.