The cottonmouth (aka water moccasin) is an opportunistic feeder, sometimes described as "omnicarnivorous". Its diet includes mammals, birds, amphibians, fish, snakes, small turtles and small alligators. These snake do not hesitate to prey on venomous like rattlesnakes or copperheads. Cannibalism is a frequent occurrence between this species as well as the feeding on carrion. But in general its diet consists of fish and frogs. Fish are captured by cornering them in shallow water, usually against the bank or under logs. They take advantage when bodies of water begin to dry up in the summer or early fall and gorge themselves on the resulting high concentrations of fish and tadpoles.
Frogs and small birds are seized and held until movement stopped. Larger prey will be approached in a more cautious manner; a rapid strike will be executed after which the snake withdraws. Young individuals have yellowish or greenish tail tips and engage in caudal luring. The tail tip is wriggled to lure prey, such as frogs and lizards, within striking distance.