Well, they do need it most of the time, but they can survive for weeks without it! Many animals would die in minutes without oxygen because it is required in the body to keep all our cells alive and working properly. Freshwater turtles (like our Painted Turtle) are able to switch to using an oxygen-free, or "anaerobic", process to keep their cells alive if there isn't enough oxygen in the water over winter hibernation. This is very risky because that anaerobic process