MIAMI (Reuters) - Shielded by an electrical field to ward off sharks, 61-year-old American swimmer Diana Nyad was pushing toward Florida Monday in her bid to set a new world record with a 103-mile crossing from Cuba without a shark cage.
"She is off to a strong start," a spokeswoman for the veteran long-distance swimmer told Reuters as she stroked and kicked toward Key West in the Florida Keys, her final destination in a marathon swim expected to last some 60 hours.
CNN producer Matt Sloane, who is on one of the boats accompanying Nyad, reported in a Tweet that the swimmer was experiencing some pain in her shoulder and "a little touch of asthma too" 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 as the sun set in a fiery glow at 7:45 p.m. EDT (2345 GMT) Sunday evening, 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, wants to be the first person to swim from Cuba to Florida without a shark cage.
She 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."
"LIVE LIFE LARGE"
She says her main aim is to help people her age and older realize they can still achieve many things.
"We all have one life and it's a one-way street, so live it, live it large," she told the "Today Show" in an interview before she set off Sunday.
Nyad said that while she swims methodically she runs her favorite songs through her mind -- music from Janis Joplin, the Beatles, Bob Dylan -- fitting the rhythm to her crawl strokes.
The athlete, who wears her light-brown hair cut short under her swimming cap and has the muscled body and broad shoulders of a marathon swimmer, has said she is not even thinking of the possibility of failure.
"You know, I just can't go there. I'd have to go into a state of unconsciousness before I not make it across," she said, displaying the steely determination that has already put her into the record books for ocean swims.
When she was years younger, Nyad swam around Manhattan in 1975 in less than eight hours and completed a 102.5 mile swim from Bimini in the Bahamas to Florida in 1979.
But none of those swims approached this one in length of time, and her longest training swim for the Florida Straits crossing was 24 hours.
Weather forecasters have predicted doldrums until Thursday in the waters that separate the United States and Cuba, giving her a good window to complete the swim.
Nyad has five boats and two kayaks alongside her, which will keep her on course as she crosses the difficult Gulf Stream current, and provide her with food and water at regular intervals.
She will be stopping each hour or so to take liquids and high-energy food, treading water. Rules for the record ocean swim attempt forbid her from touching any accompanying boat.
(Editing by Todd Eastham)