Banded Water Snake
Nerodia sipedon

Eastern 1/3 of the state.  The banded water snake is most common in clear, rocky streams. There are two subspecies in Oklahoma, the northern water snake, 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 water snakes, they are found near water, but may wander far from water in search of food, which includes fish, frogs, salamanders, and crustaceans.