If you look close you can see where the water just rolled off the big guys head. He did the classic ‘rise’ to the surface move.

Watch the gators long enough and you will notice they can just sink down and rise up, with no forward motion at all. They simply float up and down. It’s amazing, and one of the reason they seem to appear from nowhere.

An Alligator can move their rib cage, and the bodies organs, slightly from front to back. It doesn’t take much, but this effectively changes the animals center of gravity. With the change they float up and down in the water. One more reason they have been here centuries longer than people.