Just found this injteresting and related to this thread so here ya go:
Do Alligators Breathe Underwater?
Alligators can’t breathe underwater. But they can stay there for an hour or more. When an alligator submerges, or goes underwater, its heart slows down. The alligator doesn’t have to breathe as often, but the heart still pumps blood to important organs, such as the brain.
Like many animals, alligators have two eyelids to protect each eye. But when an alligator submerges, a third eyelid covers each eye. This eyelid is clear. The clear eyelids act like swim goggles.
Flaps of skin cover an alligator’s ears at all times. But when an alligator submerges, special flaps close off its nostrils and the back of its throat. Nostril flaps keep the alligator from breathing in water. The throat flap lets an alligator open its mouth to catch prey without swallowing water.
Alligators are excellent swimmers. But they don’t swim with their legs. They swim by sweeping their tails from side to side.
Couldnt find anything about how deep they go.