Why do turtles breathe air if they spend so much time underwater?

Turtles spend much of their lives in water, but they are still air-breathing reptiles with lungs. That means they must surface periodically to take in oxygen. Some aquatic turtles can remain submerged for a very long time by slowing their heart rate and reducing oxygen use, especially in cold water. A few species can also absorb limited oxygen through specialized tissues, but lungs remain essential. This is why even highly aquatic turtles must eventually come up for air.