How to Identify a Water Moccasin Water moccasins, also known as cottonmouth snakes, are venomous pit vipers found in North America. They have dark-coloured bodies with distinctive lighter bands and a thick, triangular-shaped head. Water moccasins are semi-aquatic and often found near water sources. They are known for their aggressive behaviour and the ability to open their mouths wide, displaying a white, cotton-like lining, which is why they are called cottonmouth snakes.