The 62-year-old swimmer faced stinging jellyfish, barracudas and a curious shark during her record swim attempt.
U.S. senior distance swimmer Diana Nyad is making another attempt to swim from Cuba to Florida.
So far the 62 year old has made it half way, despite being assaulted by stinging jellyfish.
Senior U.S. distance swimmer Diana Nyad swam through painful Portuguese Man O'War stings to make it half way to Florida.
Already Nyad has been swimming longer than during her last attempt to swim 103 miles of sea from Cuba to Florida. During that bid in August, shoulder pain, asthma and ocean swells forced her to abort her attempt after 29 hours.
Nyad began her journey at 6:04 pm Friday from the Ernest Hemingway International Nautical Club, just west of Havana. .
It was the 62-year-old's third try to swim the course, after failed bids in 1978 and in August. As of the last update via the Internet, she had completed 49 miles of the 103-mile passage. If all goes well, she hopes to reach Florida's coast by Monday morning.
"Now I'm in better condition than I was in August, and I'm as prepared as ever... to achieve this dream," Nyad told reporters earlier in Spanish.told Earlier Saturday, handlers saw barracudas in the area, and she was also visited by a curious shark.
"Around 1pm -- and don't everybody get excited here -- an Oceanic white tipped shark was spotted near Diana in the midst of the three boat flotilla. ... Rob MacDonald, one of (her safety) divers, swam towards the shark, where they faced off within 10 feet of one another," said a post on Nyad's website.
"I guess he thought I was more aggressive than him, and he turned in the other direction," MacDonald was quoted as saying.
Nyad hopes to become the first person to swim the stretch of ocean without a shark cage.
Australian swimmer Susie Maroney, at 22, became the first person to swim from Cuba to the United States in 1997, though she used a shark cage.
Nyad said she was ready for the 60-plus hour ordeal.
"If I could swim to the half-way point dealing with asthma, I know today that I can complete it," she said, referring to her August attempt.
Nyad tried to swim across the shark-infested straights in 1978, but gave up after 42 hours in the water due to bad weather.
"This moment is about much more than sports for me," she said, expressing hope for better ties between communist Cuba and the United States, two former Cold War foes.United The swimmer set an open sea record by swimming from the Bahamas to the Florida Keys -- a journey that is the same distance as the Cuba-Florida swim, but a feat she described as much less dangerous.
And she clinched a record for circling the island of Manhattan at the age of 50, clocking in at seven hours and 57 minutes.
As in her previous journey, five yachts and four kayaks are accompanying her, along with a 45-person support team, including trained shark divers and electronic devices designed to repel the predators.