Two subspecies of this snake are found in Illinois, the yellowbelly water snake and the copperbelly water snake. The yellowbelly water snake averages 30 to 48 inches in length, has a back that is gray or green-gray and is usually without markings, a yellow belly with a touch of orange and keeled (ridged) scales. The copperbelly water snake averages 30 to 48 inches in length, has a dark sometimes black back, a red or orange-red belly and keeled (ridged) scales.
The plain-bellied watersnake lives in river bottoms, swamps, marshes, edges of ponds and lakes. This snake is aquatic, but it may be seen basking on logs in water or along the shoreline. It may flatten its body when disturbed and/or release large amounts of nasty-smelling musk from glands at the base of the tail. Mating season occurs in April and May. Eggs are retained inside the female for development. Young are born alive in late summer, the number produced varying directly with the size of the female snake. This snake eats fishes, amphibians and crayfish.