Chris Palfrey, a long-distance swimmer himself, said the tricky currents were all that blocked his wife"s bid to become the first marathoner to make the solo crossing through the treacherous Florida Straits without a shark cage.
Such swims are referred to an 'unassisted open ocean swims,' and Palfrey captured the world record for one she made last year by swimming 67 miles (109 km) in the Cayman Islands, a Caribbean neighbor of communist-ruled Cuba.
Penny Palfrey remained strong until the aborted end of her journey, despite dehydration, muscle soreness and numerous stings from jellyfish and Portuguese man'o'war, her husband told reporters in Key West, at Florida"s southernmost tip.
"But it was the Gulf Stream currents that ultimately did her in," he said.
Palfrey, a 49-year-old grandmother, had set from Havana on Friday. She swam about 41 hours and covered 93 miles (149 km) before her swim ended at 12:06 a.m. EDT on Monday, her husband said.
That was when he and the rest of her logistical support crew advised her that the Gulf Stream was pushing her backward and she was losing ground on every stroke she took toward her elusive goal.
Palfrey was recovering on Sunday in a local hospital, dehydrated and sunburned and taking pain relief medication for numerous sores, some due to salt water exposure, and would remain under observation at least through Monday morning, her husband said.
Palfrey, who was born in Britain but lives in Australia, had hoped to complete the crossing and arrive somewhere in southern Florida within 40 to 50 hours.
Her swim followed two unsuccessful attempts last year by American marathoner Diana Nyad, now 62, to cross the Florida Straits, which in addition to strong currents are known for unpredictable weather.
The swim was completed successfully by Australian swimmer Susan Maroney in May 1997, but unlike Nyad and Palfrey, she used a shark cage.