I was with a group of Cub Scouts who were menaced by a large sick-looking Beaver swimming in the Chesapeake Bay several year ago- luckily we got all the boys out of the water
the beaver continued to stalk them, lurking just offshore like a shark, following our group up and down the beach, until he finally gave up and paddled away
Never realized how BIG those critters can get, when he first swam up and bumped a kid we thought he was a Labrador retriever
I once observed a pair of beavers swimming in the evening on the Black Warrior River adjacent to downtown Tuscaloosa. I was surprised they were around such a built-up area. They were making lots of noise slapping their tails on the water as part of their playing or courtship.