Is the northern water snake venomous?

The northern water snake is harmless. Harmless. No venom of medical significance. A bite from a large one bleeds more than you might expect because of an anticoagulant in the saliva, but it is a scratch, not an envenomation. Wash it and leave the snake alone.

How do you identify a northern water snake?

Bands are widest over the spine and pinch narrower towards the belly. A copperhead is the reverse. Swims with the body submerged and only the head above water. Cottonmouths float high and buoyant.

Where do northern water snakes live?

They are found in 36 US states, in habitats including water and wetland.

Northern Water Snake

Harmless

Nerodia sipedon · also called common water snake, banded water snake (misapplied)

The northern water snake is almost certainly the most frequently misidentified snake in North America. It is large, dark, thick-bodied, lives in water, and flattens its head when frightened — so it gets reported as a cottonmouth or a copperhead constantly, and killed for it. It is completely harmless, though it bites readily and bleeds freely when handled because its saliva contains a mild anticoagulant.

Venom: Harmless. No venom of medical significance. A bite from a large one bleeds more than you might expect because of an anticoagulant in the saliva, but it is a scratch, not an envenomation. Wash it and leave the snake alone.
Adult length: 24–42 inches (61–107 cm)
Markings: Dark crossbands at the front of the body giving way to alternating blotches towards the tail. Crucially, the bands are WIDEST across the back and narrow towards the belly — the opposite of a copperhead. Older animals darken until the pattern nearly disappears, especially when wet.
Habitat: water, wetland
Family: colubrid
Range: 36 US states

How to identify a northern water snake

Bands are widest over the spine and pinch narrower towards the belly. A copperhead is the reverse.
Swims with the body submerged and only the head above water. Cottonmouths float high and buoyant.
Flees into water when approached rather than standing its ground.
Strongly keeled scales give a rough, matte appearance rather than a glossy one.

What it does when it sees you

Basks on logs, rocks and overhanging branches and drops into the water at the first sign of a person. If cornered it will flatten its body, strike, and release a foul-smelling musk — an impressive bluff from a snake that cannot hurt you.

What the northern water snake is confused with

One test settles each of these.

Cottonmouth →

Cottonmouths gape to show a white mouth lining and float high on the surface. Water snakes do neither.

Copperhead →

Compare band shape: copperhead bands are wide at the sides and narrow on the back; water snake bands are the reverse.

Before anything else

Back away and leave it alone. A snake that can see you leaving has no reason to bite. Most bites in the United States happen to people who picked up, cornered, or tried to kill a snake.
Never handle a snake to identify it. Every identification on this site can be made from a photo or from several feet away.
If someone is bitten, call emergency services now. Keep the limb still and below the heart, remove rings and watches, and go to hospital. Do not cut, suck, apply ice, or use a tourniquet — all of these make outcomes worse.
Do not try to catch the snake for identification. A photo from a distance is enough, and hospitals treat symptoms rather than species.

In the US, the Poison Help line is 1-800-222-1222. This site is a reference, not medical advice.

Not sure it was a northern water snake? Identify it step by step →