Early Wednesday morning, an Australian swimmer took the first step in attempting a record swim from Havana, Cuba to Key West, Fla.: she jumped into the water.

No one has completed the swim Chloe McCardel hopes to complete. The closest anyone has come happened in 1997 when fellow Australian Susie Maroney completed the swim with the help of a shark cage, which helps a swimmer cut through the water and reduces the effort she must exert.

McCardel, with the help of her husband Paul McQueeney, lathered her body in a whitish sheep fat called lanolin, to protect her skin from sun damage and chaffing. She wore a black swimsuit and rubber cap.

McCardel plans to reach Key West by Friday night, a journey of 103 miles that she believes will take between 60 to 70 hours to complete. Due to the swim's immense physical demand, she will be stopping every 30 minutes to gulp down a nutrient-rich meal replacement.

The Melbourne native is no stranger to feats of extreme physical endurance. Her resume includes six solo crossings of the English Channel, two double crossings (out and back), and first place in the 28.5-mile Manhattan Island Marathon Swim in 2010. She is also a regular triathlete.

The grueling intensity of the current swim should not be understated. McCardel could burn upwards of 25,000 calories during her marathon swim. The Mayo Clinic estimates a 160-lb. person burns an average of 423 calories for every hour of swimming. In preparation for a 2010 Double English Channel Crossing, McCardel wrote on her blog that she set and achieved a goal weight of 85 kilograms, or about 187 lbs. Up from 138 lbs., she says "eating like a sumo wrestler" helped put on the extra fat necessary in insulating her from the Channel's freezing waters, a concern that is far less prevalent in the current swim.

Included with the risk of muscle fatigue is how McCardel's body will react to over 60 hours of sleeplessness. If her hopefulness is any indication, two-and-a-half days without sleep isn't enough to stop the swimmer.

"I'm really excited, I'm trying to stay calm and relaxed and just think about the finish," she told reporters Wednesday. "It'll be tough, though. It's not going to be an easy ride, but we'll get through it as a team."

In addition to her personal obstacles, McCardel also faces the hazard of less-than-friendly underwater life. Sharks, venomous box jellyfish, and inclement weather all threaten to end McCardel's swim before its natural conclusion. But despite her cageless swim, an electromagnetic field will act as a virtual cage to deter sharks from attacking.

She and her team took extensive measures to ensure McCardel had as few complications as possible. They planned the swim according to the season and moon phase to minimize the risk of box jellyfish interrupting the event — the same jellyfish that stung Diana Nyad repeatedly last year, forcing her to cut the swim short.

McCardel has assembled a small army of 50 experts in the Gulf Stream who will be monitoring the waters' every move, so that the Australian can navigate the strait as efficiently as possible.

She has great confidence in the team apparently, as she took time before jumping in on Wednesday to invite the commodore of Havana's Hemingway Marina to a party in Key West Friday night.

"I'm as confident as I can be," she said. "I think it's all going to work out well."

McCardel's swim is being done to encourage donations to cancer research, which can be made on her website www.chloemccardel.com, and to improve the longstanding tension between the United States and Cuba.