N. cyclopion is distributed from the Florida panhandle westward to Louisiana, and northward through the Mississippi Valley into southern Illinois.

[6] N. cyclopion differs from most other species of North American water snakes by having one or more small scales under the eye, giving the appearance of a ring of small plates around the eye, a character shared with the species N.

Ventrally, it is yellowish on the anterior third, and the on remainder dark brown with yellow or white semicircles.

[9] N. cyclopion prefers still waters such as bayous, lakes, marshes, ponds, sluggish streams, and swamps.

The females, which are larger than the males and have two more dorsal scale rows, may weigh over 4.1 kg (9 lb).