Water viper

Agkistrodon piscivorus, also known as the cottonmouth snake, water moccasin, or water viper, is a species of highly venomous pit viper (a type of snake) found throughout southeastern United States. Commonly called cottonmouths because of their all-white mouth, they are often confused with Northern water snakes, which are harmless, but the cottonmouth is much the opposite.
Habitat.
Cottonmouths live throughout southeastern United States, often found in water sources, such as marshes, bogs, lakes, rivers, ponds and almost every body of water you could imagine. 
Diet.
The cottonmouth's diet consists of birds, frogs, toads, lizards, smaller cottonmouths, small alligators and turtles, and a few other things. A lot of snakes eat whatever they can find. 
Venom.
Cottonmouths are one of the most dangerous snakes in the world. Remember the rhyme: if it's white, stay away! If it's not, you'll live to see another day.