U.S. endurance swimmer Diana Nyad gave up Tuesday on her latest attempt to swim from Cuba to Florida without a shark cage.

The swimmer, who on Wednesday will be 63, had completed more than half the 160-kilometer (103-mile) journey.

"Diana has been pulled from the water," her team said in a brief announcement around 8:00 a.m. EDT on the blog it has continually updated with news about Nyad's crossing.

If she had completed the feat, Nyad would have become the first person to swim across the Florida Strait without a shark cage.

She was not entirely unprotected, however - her team used an apparatus emitting electromagnetic waves to frighten the predators away.

This was the third time the veteran swimmer tried unsuccessfully to complete the challenge. In 1978 she tried it, but on that occasion had a shark cage.

Though her team has not yet explained why she called it quits, one of the main obstacles were the jellyfish, especially at night, which forced Nyad to wear an additional bathing suit to ward off the stings.

It was precisely jellyfish stings that kept her from finishing the crossing on her last attempt in September 2011.

Last Saturday Nyad set out swimming the same route for the fourth time, plunging into the open sea from Havana's Hemingway Marina tourist center bound for the Florida Keys.

Her goal was to swim the Strait in 60 hours so she could celebrate her 63rd birthday on Wednesday in Key West.

Nyad already holds the world record for longest ocean swim, a journey of 165 kilometers (102.5 miles) from Bimini in the Bahamas to Jupiter, Florida. 

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino