(CNN) -- A 49-year-old grandmother who wanted to become the first person to swim 103 miles from Cuba to the Florida Keys unassisted ended her bid early Sunday morning when a strong current in the shark-infested waters made it "impossible" for her to continue, her team said.
Penny Palfrey, an Australian-British endurance swimmer, braved jellyfish stings and the scorching sun but kept swimming since taking to the water Friday morning.
Had she been able to keep up her pace, she would have come ashore on the Florida Keys on Sunday afternoon.
But at 2 a.m. Sunday, her team said in a Facebook post that the attempt was halted.
"Penny Palfrey had to be pulled out of the water, after swimming for more than 40 hours, at approximately midnight tonight due to a strong southeast current that made it impossible for her to continue her swim," the post said. "Penny is presently on her escort boat being taken care of by her crew."
The note didn't say how far she had ultimately swum.
A post Saturday night, while Palfrey was still in the water, said she had gone more than 86 miles.
By doing so, she did score a personal best: she broke her record of 67 miles set in 2011 while swimming from Little Cayman island to Grand Cayman island.
Palfrey had wanted to become the first person to swim across the Florida straits without any assistance -- no shark cage, flippers, wet suit or snorkel.
Susie Malroney, a 22-year-old swimmer, completed the Cuba-to-the-Keys feat in 1997, but she used a shark cage.
Palfrey stayed nourished and hydrated by consuming a carbohydrate-rich drink every 30 minutes.
Her crew also employed "shark shields," cables that hang from the boats and kayaks around Palfrey and emit a pulse designed to keep the predators at bay.
"We attach (the shields) to the kayaker and to the boat which emit an electric field through the water," Palfrey told reporters in Havana on Thursday. "When a shark comes within five meters it picks up the sensors on the snout. It doesn't harm them, but they don't like it and swim away."
According to the Facebook posting on Saturday, the devices may have come in handy after Palfrey spotted hammerhead sharks swimming beneath her.
The sharks, though, "quickly vanished," according to the posting.
Last year, swimmer Diana Nyad twice tried to make the swim, also unassisted, but was turned back by health problems and stinging jellyfish.