Water Moccasin is a venomous snake, a species of pit viper, found in the southeastern United States. Adults are large and capable of delivering a painful and potentially fatal bite. When antagonized, they will stand their ground by coiling their bodies and displaying their fangs. Although their aggression has been exaggerated, on rare occasions territorial males will approach intruders in an aggressive manner. This is the world's only semiaquatic viper, usually found in or near water, particularly in slow-moving and shallow lakes, streams, and marshes. The snake is a strong swimmer and will even enter the sea. It has successfully colonized islands off both the Atlantic and Gulf coasts.
The generic name is derived from the Greek words ancistro (hooked) and odon (tooth), and the species name comes from the Latin piscis (fish) and voro (to eat); thus, the scientific name translates into “hooked-tooth fish-eater”. Common names include variants on water moccasin, swamp moccasin, black moccasin, cottonmouth, gapper, or simply viper. Many of the common names refer to the threat display, where this species will often stand its ground and gape at an intruder, exposing the white lining of its mouth.