Hard to tell from the pic, but the southeastern portion of the US is known to be the habitat of water moccasins/cotton mouths if nearby lakes/ponds are available.
Venomous and very aggressive in nature. A good way to distinguish venomous from nonvenomous is the shape of the head. If the head is more "arrowhead" shaped, as in triangular, chances are that it's venomous.
I just treat them all the same. If I come upon one, it's not like I've got enough time to figure out the shape of the head and size of the body. lol
I usually just run the other way, and most of the time the snake does to.