Can Snakes Swim? How Water Snakes, Sea Snakes and Others Swim

How do snakes swim?

A snake swims by sending waves of muscle contractions down its body from head to tail. On land, the curves of its body push against rocks, plants and bumps in the ground. In water, there is nothing solid to push against, so each bend of the body pushes water backward and to the side instead, driving the snake forward. It is much the same way an eel swims.

Snakes have a long body and no limbs to get in the way, which makes this motion efficient. A snake’s main lung is long and thin, often running along much of the body, and the air inside it works like a float. By taking a deep breath, a swimming snake stays buoyant and can rest at the surface with little effort. For more on how snakes move on land, see how snakes move without legs.

Which snakes are the best swimmers?

Many snakes are semi-aquatic, meaning they live on land but hunt and shelter in water:

• North American water snakes: the northern water snake and its relatives in the genus Nerodia rarely stray far from water. They dive to escape danger and hunt fish and frogs in the shallows.
• Grass snakes and their relatives: in Europe, the grass snake swims well and hunts frogs, newts and fish in ponds. The dice snake and viperine snake are even more aquatic and often dive for fish.
• Gartersnakes and ribbonsnakes: common North American snakes that often hunt along the water’s edge.
• The cottonmouth: a venomous pit viper of the southeastern United States that hunts in swamps, streams and ponds.
• Anacondas: the green anaconda of South America, the heaviest snake in the world, spends much of its time in rivers and swamps, where water supports its great weight.

A few freshwater snakes are almost fully aquatic. The file snakes of South and Southeast Asia, New Guinea and northern Australia have loose, baggy skin and are nearly helpless on land, spending their lives lurking on the bottom of rivers and estuaries to ambush fish.

Sea snakes: built for the ocean

The most specialized swimmers are the sea snakes. There are more than 60 species, all venomous relatives of cobras, living in warm parts of the Indian and Pacific Oceans. They include the true sea snakes, which never need to leave the water, and the sea kraits, which come ashore to rest, digest and lay eggs.

True sea snakes have several features that set them apart from land snakes:

• A paddle-shaped tail: the tail is flattened from side to side like an oar, giving strong thrust with each stroke.
• Closable nostrils: valves seal the nostrils when the snake dives.
• Breathing through the skin: some species can absorb part of the oxygen they need through their skin, helping them stay underwater for an hour or more.
• Live birth: true sea snakes give birth to live young at sea instead of laying eggs on land.

The yellow-bellied sea snake drifts in the open ocean and can barely crawl on land. Studies suggest it depends on fresh rainwater, which floats on the sea surface after heavy rain, for drinking. Sea snakes are dangerous if handled, but they are rarely aggressive, and most bites happen to people handling fishing nets.

Can snakes swim underwater?

Yes. Many snakes dive readily. A northern water snake that is disturbed while basking usually drops into the water and swims to the bottom, where it may anchor itself to plants or a submerged log. It usually stays down for a few minutes, and it can stay much longer if it has to.

Snakes can do this because, as cold-blooded animals, they use far less oxygen than mammals of the same size, especially in cool water. They cannot breathe water, though. A snake that is trapped underwater or too exhausted to reach the surface will drown, just like any other air-breathing animal.

Can a swimming position help identify a snake?

In the southeastern United States, the way a snake swims is one of the clues people use to separate harmless water snakes from the venomous cottonmouth. Cottonmouths tend to float high on the water, with the whole body riding on the surface and the head held up at an angle. Water snakes usually swim with most of the body below the surface and only the head and neck showing.

This is a useful hint, not proof. A water snake can float on the surface while resting or after a large meal, and a cottonmouth can dive. Rattlesnakes and some other land snakes also swim with their bodies floating high. The safest approach is to treat any snake you cannot identify as potentially venomous and keep your distance. For more identification clues, see cottonmouth vs water snake.

Can all snakes swim, even in the sea?

Nearly all snakes can swim if they have to, even species that live far from water. Rattlesnakes have been seen crossing rivers and lakes, and some have reached islands by swimming. Tree snakes, pythons and cobras swim well too. A few desert and burrowing snakes may rarely, if ever, have reason to swim.

Some land and freshwater snakes also cope with salt water. Cottonmouths sometimes swim between barrier islands and the mainland along the Atlantic and Gulf coasts, and several North American water snakes live in brackish coastal marshes.

Are swimming snakes dangerous to swimmers?

Most snakes seen swimming in lakes, ponds and rivers in Europe and North America are harmless and avoid people. A snake that seems to swim toward a swimmer or boat is usually just heading for the shore, a basking spot or cover. Give any snake in the water space and let it pass. If anyone is bitten by a snake that might be venomous, seek emergency medical help immediately: call 911 in the US and Canada, 112 in the EU or 999 in the UK.