if the woods where it went in have a stream or a river I'll say it's an otter.
if not then it's a coon with a colour variation.
I have bought and sold coon pups as pets, handraised and every now and then the litter contained dark pups with practically no stripes or facial masks....I even had a light grey, almost white one as well.
For a beaver it moved to fast in my opinion.

Frank