Northern Watersnake
Nerodia sipedon

Size:  2 - 3 1/2 ft
Distribution

Eastern 1/3 of the state.  The northern watersnake is most common in clear, rocky streams. There are two subspecies in Oklahoma, the northern watersnake, N.s. sipedon, found primarily in the northern counties along the Kansas border, and midland water snake, N.s. pleuralis, found elsewhere within its range. They are the only watersnake in Oklahoma that lacks a yellow belly, but instead is white and marked with red marbling or "half moons". Like all watersnakes, they are found near water, but may wander far from water in search of food, which includes fish, frogs, salamanders, and crustaceans.

Belly of the Nerodia sipedon species.