According to the Smithsonian Institution, how long a turtle can stay underwater depends on the species, locality and temperature. During hibernation, painted turtles remain underwater through the entire winter. The Fitzroy River turtle can stay underwater almost indefinitely through an adaptation of its cloaca.
The National Oceanic and Atmospheric Administration states that sea turtles can stay underwater for two hours without breathing. This assumes the animal is at rest and not active. When active, a sea turtle must return to the ocean's surface every few minutes. The leatherback sea turtle is the largest of all turtles, capable of reaching a length of 6 feet and weighing 1,400 pounds.