Endurance athlete Diana Nyad ended her swimming ultramarathon from Cuba to Florida on Sunday after medics warned another painful sting from a Portuguese Man o' War could be life threatening, Nyad team members said.

Nyad was very swollen from multiple stings to her face and body, said Vanessa Linsley, who worked on Nyad's team.

"Nobody blames her. There isn't anything that can change this … there's nothing that has to do with your swimming capabilities. You can't control mother nature," Linsley said.

The 62-year-old swimmer had completed at least 49 miles of the 103-mile passage of the treacherous Florida Straits. She soldiered through the stings, at one point cutting eye and mouth holes through a swim cap she wore over her face to prevent future stings.

But by late morning, medics warned toxins from the stings were building up and another sting could be serious.

In a Facebook posting, Nyad's team said she called out to her team from the water, saying medical experts told her not to go another two nights in the water.

According to the post, Nyad told her team: "But for each of us, isn't life about determining your own finish line? This journey has always been about reaching your own other shore no matter what it is, and that dream continues."

Linsley said Nyad was about to get out of the water and was surrounded by her support team.

Nyad was making her second attempt in as many months at the Cuba-Florida crossing, a lifelong dream that she first tried as a 28-year-old back in 1978, when she swam inside a steel shark cage for about 42 hours before ending the attempt. A cageless attempt this past August fell short in 29 hours when, gasping for breath, Nyad threw in the towel after an 11-hour asthma attack she blamed on a bad reaction to a new medicine.

Australian swimmer Susie Maroney successfully swam the shark-filled waters from Cuba through the Straits and to the Keys in 1997, though she used a cage. Nyad was trying to become the first to finish it without a cage.

Earlier in her latest swim, Nyad received oxygen and a steroid shot from her doctors and was treading water while she recovered from the stings.

After that, her team said in a website update that a so-called "staged swim record" would still be valid as long as she was on the boat only for treatment and not to rest – rather than a nonstop record.

Nyad's website said she spent the night trying to recall favorite songs and thinking upbeat thoughts while slipping through the waters under a nighttime sky bristling with stars and a sliver of a crescent moon.

The swimmer faced other obstacles aside from the man o' war stings. On Saturday, handlers spotted barracudas in the area, and she got a visit from a curious Oceanic white tipped shark that was shooed off by a support diver.

Without a cage to protect her, Nyad relied on equipment surrounding her with an electrical field that is harmless but deters most sharks. Her divers are there to gently discourage any who make it through. But not all encounters with marine life were unpleasant. Earlier in her journey, 10 pilot whales emerged in the distance ahead of the swimmer, according to one team tweet.

The Los Angeles woman regularly paused to rest and refuel on food that her assistants passed to her in the water, but without getting on the boat. To maintain her strength she ate pasta, bananas, bite-size pieces of peanut butter sandwiches, and high-calorie and high-carbohydrate drinks.