It is true that turtles breathe through their tails in a way; however they also breathe using their lungs. The type of breathing through the tail is referred to as cloacal breathing. During this breathing process the turtle pumps water into the vent called the ‘cloaca’, which in reptiles is the opening they excrete and reproduce through (two sacs) located near the tail.
The air in the water is absorbed by blood rich tissues lining the cloaca, which allows the turtle to stay underwater longer. These sacs located near the turtle’s anus are similar to the turtle’s throat as they have tiny capillary blood vessels that are equipped to absorb oxygen needed from the water.
In addition to the cloacal breathing, turtles also have a set of lungs that they can breathe with. As its activity increases so does its demand for air. The turtle, depending on the species can hold its breath underwater for a long time. Most species can hold their breath anywhere from 30 minutes to 3 hours. How long the turtle can hold its breath is also in direct proportion to how active it is and if it is able to find pockets of air. These pockets of air can be found in small caves and/or under ice.