KEY WEST (CBS4/AP) – Endurance swimmer Diana Nyad arrived in Key West late Sunday night, following a third unsuccessful attempt to to swim from Havana, Cuba, to the Florida Keys after being pulled from the water late Sunday morning because of multiple painful stings from Portuguese Man o’ War jellyfish.

According to team member Vanessa Linsley, Nyad was 54 statute miles southeast of Key West and had been swimming for more than 40 hours when she ended the marathon attempt. The entire crossing had been estimated to take approximately 60 hours.

Nyad stopped after medical experts warned her against spending more nights in the water and risking additional stings that could prove serious.

She had hoped to land in Islamorada, about 160 miles as the crow flies from Havana.

Nyad showed the stings to supporters and people who greeted her. On Saturday, she was pulled from the water for medical care, but subsequently was able to continue her swim.

“I pictured it, I really pictured it and I knew I could do it,” she cried after returning to Key West,” she said. “I wanted that feeling to be on the beach (in the Keys) so badly and it’s just not going to happen.”

Nyad’s current attempt came less then seven weeks after she aborted her second Cuba-to-Key-West try because of shoulder pain and a debilitating in-water asthma attack.

In 1978, Nyad first attempted to swim from Cuba to Florida. After being in the water for 41 hours and 49 minutes then, she had to quit because of strong currents and rough weather.

Even if Nyad was successful, she would not have been the first person to swim across the Florida Straits from Cuba to Key West. Australian swimmer Susie Maroney accomplished that in 1997.

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