The stretch of water that separates Florida and Cuba is known for its unpredictable weather, treacherous currents and big fish.
But that doesn't matter to Diana Nyad, a 61-year-old endurance athlete who hopes to be the first person in history to swim across the Straits of Florida without a protective cage.
"If I don't get eaten by a shark or just go unconscious, I will make it to the other shore," said Nyad, a legend in open-water swimming circles. "I feel pretty confident, but this is uncharted territory. I really don't know what to expect."
The 103-mile crossing could take 60 hours or longer, which is a long time for most humans to be awake, let alone swimming. But Nyad is no stranger to extreme adventures.
In 1978, she attempted the same swim but was forced out of the water after nearly 42 hours when the wind, waves and current proved too much. A year later, she successfully completed the longest open water swim in history when she stroked 102.5 miles from Bimini to Florida.
"She will have her work cut out for her," said Ron Collins, founder of the Tampa Bay Marathon Swim. "That is a long time to be in the water. There are a lot of things that can go wrong."
Long-distance ocean swimming is a solitary sport, but an athlete cannot make it alone. Everyone needs a support crew, be it a single kayaker handing out bottles of Gatorade or, in the case of Nyad, a retinue of 44 handling everything from navigation to land-based logistics. But in the end, it is the swimmer, alone in the water, with nothing but her thoughts to keep her company.
"The first thing you have to deal with is boredom," explained Randy Nutt, a veteran open-water swimmer who has circled Manhattan and Miami Beach. "You are in the water, stroke after stroke, hour after hour, and it gets kind of monotonous."
Some swimmers sing in their heads, others act out movies, line by line, or do about anything repetitive to get into "the zone."
"But conditions can change without warning," Nutt added. "All of the sudden your routine is broken and you have to adapt to a new set of variables. This throws some people off. They just can't deal with it."
Nyad knows that her mind can be her greatest asset or her biggest weakness.
"I have been training for two years and think I am in the best condition of my life," she said Tuesday from Key West. "If I do have a problem physically, hopefully my mind will be able to override my body."
Hot and cold
In most open water swims, hypothermia is the biggest danger. Cold water drains heat and energy from a swimmer's body.
Last year Collins, who successfully completed both the English Channel Crossing and the Swim around Manhattan, tried to add to his resume the third leg of the Triple Crown of Open Water, the Catalina Channel Swim in California. The water was 55 degrees, and 18 miles into a 20-mile swim, he began to hallucinate and nearly died.
"Cold water is rough," he said. "But water that is too warm can be just as dangerous."
In 2010, Fran Crippen, a 26-year-old member of the U.S. national team and former star at the University of Florida, died while competing in an open water race in Dubai. Details were sketchy but several contestants said the water temperature was in the upper 80s, dangerous territory for a swimmer working hard.
The annual 12.5-mile Swim around Key West, held each June, is a notoriously hot race that can leave participants close to heat exhaustion.
"You get above 87 degrees and you shouldn't be racing," Collins said.
The water temperature in the Straits of Florida is hovering around 86 or 87 degrees, said Alyce Tordsen, one of Nyad's logistical coordinators. "We don't want 85 . . . that is too cold," she said. "And we don't want 89 … that is too warm. It has to be just right."
Nyad can also count on stings from sea lice, jelly fish, bloody chafing on her arm pits, chest and legs, as well as saltwater leaving her tongue swollen and sore. These are minor inconveniences that come with any long, open-water swim.
Any fishermen who has trolled outside the reef line off Key West knows better than to get in the water. The area is known for its big sharks.
In 1945, one of the largest great whites on record was caught in the very waters where Nyad will be swimming. This fish, widely known as the "Cuban Shark," reportedly measured 21 feet.
Swimming in deep water can be unnerving. Even under ideal conditions, you can only see 40 or 50 feet down. Large fish appear as shadows and it is impossible to tell which direction they are moving.
Nyad will be swimming at least half of the time in total darkness. "It is a whole different ball game at night," said Collins. "You know there are things down there, some with big sharp teeth, checking you out. But what can you do except keep going?"
A team of six kayakers, one of whom will carry an electronic device to repel sharks, will accompany Nyad on the crossing.
"We are confident the shark shield will work," said Tordsen, who will be on Nyad's 32-foot support boat. "We'll also have some divers in an inflatable raft who will actually get in the water and chase any sharks away if there is a need."
Nyad and her crew are most worried about the weather.
"We want it to be calm," Tordsen added. "We don't want the wind to be blowing any more than 5 or 6 mph."
Under the best circumstances, Nyad will cover about two miles each hour. She will actually have to swim slightly west to take into account the power of the Gulf Stream, which will be pulling her east. But a stiff head wind could easily cut her progress in half, and if that happens, she will be on the losing end of a numbers game.
"It could take three days," Nyad said. "Nobody has ever swam that long before. I don't know how long my body will hold out in that case."
Then there is the age factor. At 61, Nyad is older than most endurance athletes.
"Age doesn't matter," said 80-year-old Judge Robert Beach, a St. Petersburg swimming icon who recently did back-to-back swims in the Turks and Caicos. "Swimmers may not necessarily get faster, but they do get better with age.
"If she is going to make it," he said, "wisdom and experience will be the things that carry her through."
Terry Tomalin completed the 12.5-mile swim around Key West in 1995. He can be reached at firstname.lastname@example.org or (727) 893-8808.