Northern Water Snake (Nerodia sipedon): Facts, Habitat and ID

What does a northern water snake look like?

The northern water snake is a thick-bodied snake with a broad, slightly flattened head, small eyes with round pupils and rough, keeled scales. Keeled means each scale has a small ridge down the middle, which gives the skin a dull, matte look rather than a glossy one. The background color ranges from light gray or tan to reddish brown, dark brown or almost black.

The pattern is the best clue. Near the head, dark brown or reddish bands cross the back; farther along the body they break up into alternating blotches on the back and sides. The lip scales usually carry dark vertical bars. The belly is white, yellow or orange, typically marked with reddish or black half-moon shapes.

Young water snakes have the crispest pattern, with sharp reddish-brown or dark bands on a pale gray or tan background. As the snake ages, the background darkens and the bands fade, so many old adults look plain brown or blackish, especially when dry. When the snake is wet and in sunlight, the bands often show again. These big, dark adults are the ones most often mistaken for cottonmouths.

The species belongs to Nerodia, the genus of North American water snakes, which has about nine or ten species. Its official standard English name is common watersnake, but most people know it as the northern water snake, a name that strictly belongs to the subspecies N. s. sipedon. The other subspecies are the midland water snake (N. s. pleuralis) of the Midwest and South, the pale, faintly marked Lake Erie water snake (N. s. insularum) and the dark Carolina water snake (N. s. williamengelsi) of coastal North Carolina.

How big do northern water snakes get?

Northern water snakes are medium to large snakes. Adults usually measure 61–140 cm (24–55 in) in total length, and females are clearly bigger and much heavier than males. In one study, adult females averaged about 81 cm (32 in) and males about 70 cm (27.5 in).

Their heavy build makes water snakes look bigger than they are. A thick, dark snake of 1 m (3.3 ft) basking on a log can seem enormous, which feeds many exaggerated stories about giant “moccasins”.

Where do northern water snakes live?

The northern water snake lives across eastern and central North America. Its range runs from southern Ontario, southern Quebec and Maine south to the Gulf states and the Florida Panhandle, and west to eastern Colorado, Nebraska, Kansas, Oklahoma and northern Texas. In the coastal lowlands of the Southeast, other water snakes such as the banded water snake (Nerodia fasciata) largely take its place. An introduced population, probably started from released pets, has been found near Roseville in northern California.

It uses almost any permanent fresh water: rivers, streams, lakes, ponds, marshes, swamps, bogs, canals, ditches and reservoirs. It prefers calm or slow-moving water with plenty of places to bask, such as rocks, logs, overhanging branches, dams, docks, beaver lodges and dry cattail stems. Young snakes often stay in smaller streams and shallow edges, away from the large fish, herons and turtles of open water.

In the north, water snakes are active from about April to October. They spend the winter dormant in rock crevices, burrows, stone walls, dams and muskrat or beaver lodges, often close to water and sometimes with other snakes.

What do northern water snakes eat?

Northern water snakes are carnivores that eat mainly fish and amphibians. Typical prey includes minnows, shiners, sunfish, small catfish, frogs, toads, tadpoles and salamanders, plus crayfish, leeches and large insects. Now and then they take small mammals, birds or dead fish.

They hunt by sight and smell, searching along the water’s edge, probing among plants and under stones, and sweeping their open mouths through schools of small fish or tadpoles. At night they often catch small fish resting in shallow water. Water snakes are not constrictors: they grab prey and swallow it alive, usually headfirst. On the Lake Erie islands, the invasive round goby now makes up most of the Lake Erie water snake’s diet. There is more detail in What do water snakes eat?.

Behavior and defense

Northern water snakes can be active by day or night. In spring and fall they bask for long periods in the sun, while in hot summer weather they often hunt after dark. They are mostly solitary, although several may share a good basking spot or a winter den.

They are excellent swimmers and divers, and they rarely move far from water. A disturbed water snake usually drops from its perch with a splash and swims away or dives to the bottom, where it can wait for several minutes or longer. You can read more about how they do it in Can snakes swim?.

If cornered or picked up, the northern water snake defends itself vigorously. It flattens its head and body, which makes the head look wide and triangular, then strikes and bites repeatedly. It also smears its attacker with foul-smelling musk and droppings, and may bring up its last meal. The bite is painful and bleeds freely because of a mild anticoagulant in the saliva, but the snake is not venomous; see Are water snakes venomous?. There are also records of water snakes losing part of the tail when grabbed by it; unlike a lizard’s tail, it does not grow back.

Reproduction and live birth

Northern water snakes mate from about April to June, often near their winter dens. Males find females by scent, and a female frequently mates with more than one male, so a single litter can have several fathers.

Like other North American water snakes, this species gives birth to live young instead of laying eggs. The eggs stay inside the mother’s body, and the young are born in late summer or early fall, from about late July to early October depending on the region. Litter size depends strongly on the mother’s size: litters from 4 to as many as 99 young have been recorded, and bigger females have bigger litters. A few cases of virgin birth (parthenogenesis) have been documented in captive females.

The newborns are 19–27 cm (7.5–11 in) long and get no care from their mother. They can swim and hunt from birth, starting with small fish and tadpoles. Males can breed at about 21 months old, and females usually from about three years.

Lifespan and predators

How long northern water snakes live in the wild is not well known. The longest documented lifespan is about nine years and seven months, for a snake in captivity. Many young snakes die in their first year, eaten by herons, hawks, raccoons, skunks, opossums, foxes, snapping turtles, large fish such as bass, and other snakes, including racers and milk snakes.

People are a major cause of death too. Water snakes are killed on roads, especially near wetlands, and many are killed on sight by people who believe they are cottonmouths.

Northern water snake vs cottonmouth

The northern water snake is the snake most often mistaken for the cottonmouth, or water moccasin, a venomous pit viper of the southeastern United States. The ranges overlap only in the South: cottonmouths live from southeastern Virginia to Florida and west to central Texas, reaching north along the Mississippi Valley to southern Illinois. There are no cottonmouths in states such as Pennsylvania, New York, Ohio and Michigan, or anywhere in Canada.

None of these signs is foolproof from a distance, and the safest rule is never to approach any snake closely enough to check its eyes. For a full side-by-side guide, see cottonmouth vs water snake.

Conservation status

The northern water snake is listed as Least Concern on the IUCN Red List. It is common and widespread, and it tolerates farm ponds, reservoirs and city parks as long as there is water and food. Local threats include the draining and development of wetlands, road traffic and deliberate killing.

The Lake Erie water snake is a conservation success story. This subspecies lives only on the islands of western Lake Erie, in Ohio and Ontario, and it declined sharply as people killed snakes and built over shorelines. It was listed as threatened in the United States in 1999, when the population was estimated at roughly 1,500 adults. Habitat protection, public education and a new food supply, the round goby, helped numbers rise to nearly 12,000 by 2009, and the U.S. Fish and Wildlife Service removed it from the federal list in August 2011.

Myths and relationship with people

The most common myth is that water moccasins live in northern lakes and rivers. In the northern states and Canada, a thick, dark, banded snake in the water is almost always a northern water snake. Another myth is that water snakes chase people. A snake swimming toward a swimmer or boat is usually heading for a basking spot or cover, or has not noticed the person.

Many anglers also believe water snakes ruin fishing. In reality they mostly catch small, slow, sick or very abundant fish, and they are prey themselves for many animals, so they are a natural part of healthy ponds and streams. In California, where they were introduced, they are a concern because they may compete with or eat native species, including the threatened giant garter snake.

The best way to enjoy northern water snakes is to watch them from a distance as they bask on rocks and logs on a sunny spring morning. Left alone, they quickly slip into the water and pose no danger to people.