Are Water Snakes Venomous? Harmless Water Snakes Explained

Are water snakes venomous or poisonous?

Water snakes are neither. A venomous animal injects toxins, usually through fangs or a sting, while a poisonous animal is harmful to touch or eat. Water snakes have no venom-delivering fangs, and they are not toxic to touch.

Their mouths hold rows of small, sharp teeth that curve backward. These teeth are perfect for gripping slippery fish and frogs, which the snake then swallows alive. A water snake has nothing like the long, hollow, folding fangs of a pit viper, which work like hypodermic needles.

The word “water snake” is often used loosely for any snake seen swimming. In this article it means the true water snakes of the genus Nerodia, which live only in North America, plus the similar harmless species of Europe.

Why do water snake bites bleed so much?

People bitten by a water snake are often surprised by how much the wound bleeds. There are two reasons. First, a large water snake has dozens of sharp teeth, and as it bites and pulls away, it can leave several rows of small cuts. Second, its saliva contains a mild anticoagulant, a substance that slows blood clotting, so the scratches keep bleeding for a while.

This is not venom. The anticoagulant has no meaningful effect on people beyond messy scratches. Water snake bites are painful and unpleasant, not dangerous in the way a cottonmouth or rattlesnake bite is.

Why water snakes seem dangerous

Water snakes have an impressive defense routine, and it convinces many people that they must be venomous. A cornered water snake flattens its head and body, which makes the head look wide and triangular like a viper’s. It strikes repeatedly, bites hard if grabbed and smears its attacker with foul-smelling musk and droppings. It may also bring up its last meal.

All of this is a bluff backed by teeth, not venom. Given the chance, a water snake almost always escapes instead, dropping from its basking spot into the water and diving out of sight. Most bites happen when people try to pick up, pin or kill the snake.

Which water snakes live in North America?

All North American water snakes are nonvenomous. The best-known species include:

• Northern or common water snake (Nerodia sipedon): the widespread species of the East and Midwest, from southern Canada to the Gulf states.
• Banded or southern water snake (Nerodia fasciata): common in the southeastern coastal plain, including Florida.
• Plain-bellied water snake (Nerodia erythrogaster): a plain-backed species with a yellow, orange or reddish belly, found from the Midwest to Texas and the Southeast.
• Diamondback water snake (Nerodia rhombifer): a heavy-bodied snake of the Mississippi Valley and south-central states, with a chain-like pattern.
• Brown water snake (Nerodia taxispilota): a large, dark-blotched snake of southeastern rivers that often basks on branches over the water.
• Green water snakes (Nerodia cyclopion and Nerodia floridana): plain greenish snakes of southern swamps and marshes.

Other harmless snakes also swim well, including gartersnakes, ribbonsnakes and queen snakes. In Europe, the grass snake, barred grass snake, dice snake and viperine snake fill the same role. The viperine snake even mimics a viper by flattening its head and hissing, but it is harmless.

How to tell a water snake from a cottonmouth

The cottonmouth, also called the water moccasin, is a venomous pit viper of the southeastern United States. Its range runs from southeastern Virginia to Florida and west to central Texas, reaching north along the Mississippi Valley to southern Illinois. It does not live in the northern states or Canada, so across much of the northern water snake’s range a snake in the water cannot be a cottonmouth.

Where the two overlap, these signs help:

No single sign is completely reliable, and checking pupils means getting far too close. When in doubt, treat the snake as venomous and give it space. The full guide is cottonmouth vs water snake.

Which venomous snakes do go in the water?

The cottonmouth is the only North American viper that regularly hunts in water, but other venomous snakes can swim. Copperheads sometimes live along streams, rattlesnakes swim across rivers and lakes, and the eastern massasauga, a small rattlesnake, lives in wet meadows and fens around the Great Lakes. Sea snakes are highly venomous, but they live in tropical oceans, and only the yellow-bellied sea snake very rarely drifts as far north as southern California. For an overview, see venomous snakes in the US.

Staying safe around water snakes

Water snakes are best enjoyed from a few steps away. Do not try to catch, corner or kill a snake you find near water: that is when nearly all bites occur, whatever the species. Keep children and dogs back and let the snake leave on its own, which it usually does within seconds.

If anyone is bitten by a snake that might be venomous, seek emergency medical help immediately: call 911 in the United States or Canada.