Cottonmouth viper (Agkistrodon piscivorus) – 7 mph (11 kph) Commonly known as the water moccasin, the cottonmouth viper is native to the Southeastern United States, typically in or near water.

Water moccasins and cottonmouths are actually the same venomous species (Agkistrodon piscivorus), despite the common misconception that they are different snakes with varying levels of danger.