Both copperheads and water snakes can swim well. Though all snakes swim on top of the water, poisonous water snakes can float when they stop. All snakes swim and few snakes dive, some of the most venomous snakes in the world however dive below the water and swim there as opposed to on the surface. Harmless Watersnake or Venomous Water Moccasin? Water snakes may float or swim at the surface of the water, and at times cottonmouths will swim underwater to capture fish. Both Copperheads and Cottonmouths fill their lungs with air prior to entering the water causing them to float high in the water. There is one snake that is the exception to many of the above rules. Conversely, water snakes typically swim at or under the surface of the water, with their heads level with their bodies. All snakes swim and few snakes dive, some of the most venomous snakes in the world however dive below the water and swim there as opposed to on the surface. Unfortunately, many individuals presume that if a snake swims in the water, then it must be a water moccasin. It's easy to get the two confused, and many, many water snakes have been killed by mistake. Garter snakes swim very well, and will often enter the water to escape predators. In our region they swim both in fresh and brackish water. They also have a similar diet, though the water snakes tend to eat more minnows, crayfish, salamanders, etc. Perhaps one of the most misunderstood and mistreated species of the snake lives in water. A poisonous snake will skim along the top of the water. Take a look at the pictures below. Are Water Moccasins Aggressive?

Exceptions exist, however. Do Poisonous Water Snakes Swim and Float?
The coral snake is a very poisonous snake but does not have a heat sensor, triangular face, or slit-like pupils. The snakes have ranged from black snakes to moccasins and one copperhead. On the contrary, non-venomous snakes sink below the surface when stationary. While all snakes can swim in water, only a small percentage of snakes … Cottonmouths (Agkistrodon piscivorus).Sadly, harmless snakes are often killed out of fear for the safety of family and pets.
Their head is the only part of their body that can be seen above the water. Eastern Coral Snakes: “Red on Yellow, Kill a Fellow…“ There are several types of coral snakes, but today we are focusing on the eastern coral snake. "If you encounter a snake on top of the water like the snake seen below, this is a good indicator of a venomous snake," reads the post. There are many harmless watersnakes (genus Nerodia) that are frequently confused with venomous Water Moccasins a.k.a. Ribbon snakes (Thamnophis sauritus) are close relatives of garter snakes, and similar to them in terms of both appearance and their adoption of a semi-aquatic lifestyle. This is because venomous snakes swim with their lungs inflated, whereas a harmless water snake will swim with its body submerged. What can we do to try to eliminate snakes in the water adjacent to the shore and dock to make swimming safe for ourselves and guests? A non-poisonous snake will swim with its body submerged, with its head popped up from the water line. Also known as a water moccasin, cottonmouth snakes swim on top of the water, like several other varieties of water snakes.