Cottonmouth
Agkistrodon piscivorus
Size:  4 - 4 1/2 ft
Distribution
Eastern 1/3 and southern part of state from southern Seminole Co. to west of Waurika.  The cottonmouth, or water moccasin, gets its name from the cottony-white lining of its mouth, which it displays as a threat to an intruder.  Known to be highly aggressive, this snake, like most snakes, will usually avoid confrontations with people.  The venom is extremely potent and could be considered lethal given the appropriate circumstances.
These pictures are of a large western cottonmouth (A. p. leucostoma) between 3 1/2 to 4 ft, caught at Ten Acre Rock just south of Mill Creek, April 2004.