Yep, that triangle head and hooded eyes are a dead givaway. but the patterning on the back looks a lot like the non-venomous diamond back water snakes we have around here..
Dont let the triangle head fool you. While pit vipers (Copperheads, rattlers, moccasins) all have a triangle head, a lot of harmless watersnakes do as well.
The give away on a cottonmouth is the dark horizontal band across the eye. I dont care if the snake is old and hardly has any pattern, or if it's a new born that still has a yellow tail (GIVE AWAY FOR A JUVY COPPERHEAD OR COTTONMOUTH!!!!, yellow tip of the tail!!), it will still have the dark horizontal band across the eye.
But yes, cottonmouth.