Endurance swimmer Diana Nyad has begun her fourth attempt to swim from Havana, Cuba, to the US Florida Straits without a shark cage.
The American, who turns 63 this week, is being accompanied by five boats and 50 crew members, including divers with extensive shark experience and jellyfish experts, on the 103-mile swim.
Her previous attempts were thwarted by wind, waves, asthma, shoulder pains, jellyfish and the threat of sharks.
She abandoned her most recent attempt in September 40 hours in, after medics warned she had suffered dangerous jellyfish stings.
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Previous attempts in 1978 and in August 2011 were also called off, while unfavorable weather forced her to call off a planned crossing during the summer of 2010 before she even set out.
"You have to learn from your mistakes. You don’t do it the first time," the Associated Press quoted Nyad as saying at a news conference.
"We need some luck, but we do feel like we’ve solved all the problems."
According to Reuters, Nyad had planned to begin the swim on Sunday morning, however forecasts of rising winds forced her to bring forward the attempted crossing.
Waters at the Havana yacht club Marina Hemingway were choppy at the start of her swim, and according to Sky News, she admitted to feeling nervous.
"I think it's healthy. When you have a respect for something, you have some fear," she said.
"There is some fear, but there's also courage, and these three days, I need the courage to be stronger than the fear."
However, she told NBC: "What should I do, quit? That's not me, I'm not a quitter. I'm not going to quit until I stand on the shore in Florida."
Nyad had chosen to traverse the powerful Gulf Stream, flowing due east through the straits, instead of a more northerly course that would nudge her toward the Florida Keys.
She was refusing to use a shark cage because the device boosted a swimmer's strokes, according to Sky.
According to the AP, Nyad signaled the start of her latest attempt by pointing to the open water, blowing a bugle and crying: "Adios amigos! Courage!"
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