N. fasciata is natively found from Indiana, south to Louisiana, and east to Florida. Adults of the banded water snake measure from 24 to 42 in in total length, with a record size (in the Florida subspecies) of 62.5 in in total length.
It is typically gray, greenish-gray, or brown in color, with dark crossbanding. Many specimens are so dark in color that their patterning is barely discernible. The ventrum (belly) is typically an off-white to white. They have flat heads, and are fairly heavy-bodied. Banded water snakes may also be identified by a dark stripe which extends from the eye to the angle of the jaw. If irritated, they release a foul-smelling musk to deter predators.