The crayfish, also know as a crawdad, looks much like a small lobster. However, crayfish only live in fresh water, and they grow to be about 6 inches in length. There are many different species of crayfish, in fact around 350 species can be found just in the United States. These invertebrates live in water, and when things start to get dry they dig a burrow. You might see their mud chimney while walking beside a body of water..