A leatherback turtle called Billie won the first Great Turtle Race from Costa Rica to the Galapagos Islands, swimming at a leisurely 5 to 6 kilometres per hour, organisers say.
Satellite tracking of 11 tagged turtles showed Billie sprinting away from the main group to make it first to the finish zone.
Two turtles failed to get past the starting line, and another, Purple Lightning, veered miles off course.
Some 600,000 people logged on to the web site of the two-week Pacific Ocean marathon , aimed at drawing attention to the endangered species whose numbers have plummeted 95 per cent over the past 20 years.
The coffee table-sized turtles, which were around at the same time as dinosaurs, are dying in accidental captures by long-line fishing boats and losing nesting areas because of coastal development, said Lisa Bailey, spokeswoman for Conservation International, one of the race organisers.
At Playa Grande, a key nesting ground in northern Costa Rica where the race started, only 50 turtles showed up to lay eggs this year, down from 1,500 in 1989, Bailey said.
The 805-kilometre race was a virtual replay of the tracks of turtles that were tagged and released at different times last February for their annual migration.
Sponsors paid $US25,000 to back a turtle, $US10,000 of which went for the satellite tracking tag. Some of the money will be used to buy nesting land and save it from developers.
Ms Bailey said the information gathered in the race would have a scientific purpose. "This is no publicity stunt," she said.