Water snakes are any of a large number of snakes that swim and hunt in the water. Water snakes can be found throughout the world, and although not often poisonous, when they are they can be some of the most poisonous snakes in the world. For this reason, care should be taken when faced with an unknown water snake.

Although all snakes can swim, some are particularly at home in the water. These snakes, which include cottonmouths, Northern water snakes, Asiatic water snakes, Rainbow water snakes, and mangrove snakes, can be very dangerous for hapless bathers or swimmers. At the same time, water snakes have nothing to propel off of, making their strikes much slower.

Most snakes, even water snakes, are simply not as effective in combat when off land. For this reason, they will tend not to attack unless provoked. For the most part, water snakes will run away rather than fight. That said, if a snake feels threatened or cornered, or is accidentally jarred, it will likely lash out. In the case of some water snakes, such an event can be deadly.

The best thing to do to avoid undesired encounters with water snakes is to stay away from places where water snakes like to sun themselves. Primarily, this means overhanging tree branches. Many water snakes lie up on the branches to gather sunlight, and then drop down into the water if they detect motion. They’re not dropping to attack, they’re actually trying to run away, but if they happen to land in a boat or on a swimmer, they can panic and attack.

In North America, only one of the water snakes is poisonous: the cottonmouth water moccasin. Water moccasins are related to rattlesnakes and copperheads, and can be deadly poisonous. They have trapjaws which can snap shut quickly and with great force, driving its venomous fangs deep into flesh. Their name derives from their habit of lying with their mouths agape, showing the white interiors. Although often maligned as being aggressive, water moccasins are actually fairly docile. Generally, water moccasins will avoid humans, unless provoked in some way.

A number of non-poisonous water snakes live in North America as well. These include the Florida green water snake, the diamondback water snake, the brown water snake, the salt marsh snake, the plainbelly water snake, and the southern banded water snake. None of these water snakes are aggressive or poisonous, but as a number of them are at least somewhat similar in appearance to water moccasins, care should be taken anyway, unless identification is certain.

In South America one of the most prevalent water snakes is the mangrove snake from Venezuela and the islands of Trinidad, Tobago, and the Guianas. Although not poisonous, mangrove water snakes are fairly easily provoked, and their bite is painful and can cause infection. The Asiatic water snake, found throughout South-East Asia, China, Indonesia, and parts of Western Asia, is another non-venomous water snake. Asiatic water snakes are quite docile, and will rarely attack unless extremely provoked.