Diana Nyad
Diana Nyad after she was pulled from the water.

Endurance swimmer Diana Nyad has ended her fourth bid to swim from Cuba to Florida after four days of storms, jellyfish stings and shark threats.

Nyad's support team posted on her blog that the athlete made the call after being pulled from the water a day before her 63rd birthday.

The New Yorker, a prolific journalist and author, left Havana on Saturday in her third attempt since last year to become the first person to swim the Florida Straits without a shark cage. She has also previously tried, and failed, to swim the entire stretch in a cage.

Only one woman, Australian Susie Maroney, has ever successfully swum the 103-mile Straits, and she used a cage to do so.

Nyad made a good start to her attempt, and managed to keep going for four days despite multiple jellyfish stings, before swimming into the middle of a storm around 55 miles off the coast of Key West - forcing her support team to pull her from the water.

Despite suffering swollen lips and hypothermia, Nyad initially wanted to return to the water. However, after listening to her support team, she eventually agreed to return to Key West by boat.

Preparation

Nyad had trained for three years in preparation for the feat. She was accompanied by a support team in boats, and a kayak-borne apparatus shadowing Nyad helped keep sharks at bay by generating a faint electric field that is not noticeable to humans.

A team of handlers was always on alert to dive in, and distract any sharks that made it through the electric field.

During her marathon swims, Nyad takes periodic short breaks to rest, hydrate and eat high-energy foods such as peanut butter.

Storm Florida