N
Species Profile

Northern Water Snake

Nerodia sipedon

Not a cottonmouth-just a water snake.
iStock.com/IcemanJ

Northern Water Snake Distribution

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Found in 33 states/provinces

northern water snake curled up in leaves

At a Glance

Wild Species
Also Known As Common water snake, Water snake, Brown water snake, Black water snake, Water adder
Diet Carnivore
Activity Diurnal+
Lifespan 6 years
Weight 0.5 lbs
Status Least Concern
Did You Know?

Adult total length commonly 61-140 cm (Ernst & Ernst, 2003).

Scientific Classification

The Northern Water Snake (Nerodia sipedon) is a robust, nonvenomous, semi-aquatic snake native to much of eastern and central North America. It is frequently encountered along freshwater habitats and is often misidentified as a venomous cottonmouth.

Kingdom
Animalia
Phylum
Chordata
Class
Reptilia
Order
Squamata
Family
Colubridae
Genus
Nerodia
Species
Nerodia sipedon

Distinguishing Features

  • Nonvenomous, thick-bodied water snake with variable banded/blotched patterning that may darken with age
  • Strong association with freshwater; often seen basking near shorelines
  • Round pupils and lack of a facial heat-sensing pit (unlike pit vipers such as cottonmouths)
  • Often flattens head/defensively postures and may emit musk when handled; behavior can contribute to venomous-snake misidentification

Physical Measurements

Males and females differ in size

Length
♂ 2 ft 7 in (1 ft 10 in – 3 ft 7 in)
♀ 2 ft 11 in (1 ft 12 in – 4 ft 7 in)
Weight
♂ 0 lbs (0 lbs – 1 lbs)
♀ 1 lbs (0 lbs – 3 lbs)
Tail Length
♂ 6 in (4 in – 9 in)
♀ 7 in (4 in – 10 in)
Top Speed
2 mph
swimming

Appearance

Primary Colors
Brown Gray
Secondary Colors
Black Cream Red
Skin Type Nonvenomous colubrid with strongly keeled dorsal scales (rough texture); semi-aquatic body with smooth ventral scutes for traction; skin often appears glossy when wet.
Distinctive Features
  • Robust, heavy-bodied water snake; adult total length commonly 61-107 cm, with maximum reported about 140 cm (Ernst & Ernst, 2003; species accounts).
  • Head only moderately wider than neck; often flattens head defensively, which can mimic a viperlike shape.
  • Lacks heat-sensing facial pits and has round pupils (helps distinguish from cottonmouth, Agkistrodon piscivorus).
  • Typically shows dark vertical bars on upper lip scales; cottonmouths more often show a bold facial mask/stripe in juveniles and different head scalation.
  • Belly commonly patterned with dark half-moons/checkering; cottonmouth bellies are usually plainer and overall body often more uniformly dark in adults.
  • Semi-aquatic freshwater habitat use: frequently basks on logs/rocks and drops into water when approached; swims with head above water.
  • Foraging/hunting: primarily active hunting in shallow water and along shorelines; diet dominated by fish and amphibians (documented across multiple field studies and summaries).
  • Defensive behavior: readily bites if handled; may release musk and feces; frequent source of "venomous" misidentification despite being nonvenomous.
  • Regional pattern variation: band width/contrast and overall darkness vary across the range; large adults often show reduced visible banding due to melanism.
  • Longevity: reported to reach roughly 9-10 years in the wild and 15+ years in captivity in compiled species references (e.g., Ernst & Ernst, 2003; husbandry records).

Sexual Dimorphism

Females average larger and heavier than males at maturity, while males tend to have proportionally longer tails (hemipenal region). Both sexes share similar coloration and pattern, though large females may appear darker due to greater average size/age.

♂
  • Typically smaller adult body length and mass than females (population-dependent).
  • Proportionally longer tail base and tail length due to hemipenes.
  • Often mature at smaller size than females in many populations.
♀
  • Typically longer and heavier-bodied than males; more robust midbody girth.
  • Often show more frequent extreme adult darkening simply because they reach larger sizes/older ages.
  • Shorter tail relative to body length than males.

Did You Know?

Adult total length commonly 61-140 cm (Ernst & Ernst, 2003).

Newborns are live-born (no eggs laid) and measure about 18-25 cm at birth; litters commonly 12-36, with reported extremes of 4-44 (Ernst & Ernst, 2003).

They often darken with age (ontogenetic darkening), so older adults can look nearly uniform dark brown/black even if juveniles were strongly banded.

Their strongly keeled scales give them a "rough" texture-helpful for gripping slippery prey and wet surfaces.

Northern Watersnakes are famous for defensive musking: they may release a strong-smelling cloacal secretion when handled.

They are powerful fish-and-frog hunters that frequently forage along shorelines and in shallow water, striking and holding prey rather than constricting (Ernst & Ernst, 2003).

A subspecies, the Lake Erie Watersnake (Nerodia sipedon insularum), became a well-known conservation success and was removed from the U.S. Endangered Species List in 2011 (USFWS).

Unique Adaptations

  • Semi-aquatic head design with valvular nostrils that can close during submergence, reducing water entry while hunting underwater (functional morphology noted for natricine water snakes; see Ernst & Ernst, 2003).
  • Strongly keeled dorsal scales improve traction on wet rocks/logs and help hold slippery fish and amphibians.
  • Live-bearing (viviparity) allows reproduction without egg incubation sites-an advantage in cool, wet shoreline environments (Ernst & Ernst, 2003).
  • Pattern variability across its range (bands, blotches, overall darkness) provides camouflage in different freshwater settings (muddy rivers, rocky lakeshores, vegetated marshes).
  • Robust body and strong jaw musculature suited to wrestling active aquatic prey rather than relying on constriction.

Interesting Behaviors

  • Shoreline ambush and active foraging: patrols edges of lakes, rivers, ponds, and marshes, striking at fish and amphibians in shallow water (Ernst & Ernst, 2003).
  • Basking behavior: commonly seen coiled on branches, rocks, logs, or riprap near water; drops into the water when approached.
  • Defensive repertoire: flattens the body, strikes repeatedly, and releases musk/feces; will bite readily if grabbed (not venomous) (Ernst & Ernst, 2003).
  • Seasonal cycles: enters winter dormancy in frost-free refuges (rock crevices, mammal burrows, foundations); may overwinter communally where suitable shelter exists.
  • Ontogenetic color change: juveniles show bold crossbands/blotches; adults often appear darker, which can increase misidentification risk.
  • Prey handling: typically holds struggling prey in the jaws and swallows headfirst; larger fish may be hauled to shore for leverage (reported in field observations summarized by Ernst & Ernst, 2003).
  • Human-tolerant habitat use: readily occupies human-altered freshwater edges (marinas, retaining walls), which increases encounters and mistaken-identity conflicts.

Cultural Significance

Northern Watersnakes (Nerodia sipedon) are often wrongly called 'cottonmouths,' causing needless killing of this nonvenomous native snake. The Lake Erie Watersnake subspecies was delisted in 2011 (USFWS) and shows coexistence and care of freshwater shores.

Myths & Legends

In Great Lakes Ojibwe (also called Chippewa) traditions, the "Underwater Panther" is described as a powerful water spirit associated with deep lakes and rivers and linked with dangerous waters and storms.

In Cherokee tradition, a great horned serpent is associated with rivers and hidden places; while not a tale about Nerodia specifically, watersnakes along streams can evoke such river-serpent stories.

Iroquoian and wider Eastern Woodlands "Horned Serpent" motifs portray serpents as potent beings of water and the underworld; sightings of large shoreline snakes have historically been folded into these broader serpent narratives.

Early North American river stories often called harmless watersnakes 'water moccasin.' Over time this wrong name stuck as a local label for Nerodia sipedon whenever people expected a dangerous moccasin near water.

On the Lake Erie islands, 20th-century local anecdotes often spoke of 'swarms' of big watersnakes along rocky shores-stories that later intersected with public debates and eventual pride around the Lake Erie Watersnake's recovery and return.

Conservation Status

LC Least Concern

Widespread and abundant in the wild.

Population Stable

Life Cycle

Birth 23 neonates
Lifespan 6 years

Lifespan

In the Wild
2–9 years
In Captivity
10–21 years

Reproduction

Mating System Polygynandry
Social Structure Aggregation Group
Breeding Pattern Transient
Fertilization Internal Fertilization
Birth Type Internal_fertilization

Solitary most of year but forms spring/fall mating aggregations; several males may court a single female ("mating ball"), and both sexes mate multiply. Internal fertilization; females give live birth in late summer (typical litter ~23, reported range 4-74).

Behavior & Ecology

Social Aggregation Group: 1
Activity Diurnal, Crepuscular, Nocturnal
Diet Carnivore Small freshwater fish (reported as the dominant prey category in most field diet summaries for Nerodia sipedon; e.g., Ernst & Ernst 2003; Gibbons & Dorcas 2004).
Seasonal Hibernates

Temperament

Generally wary and secretive; usually flees into water when approached (Ernst & Ernst, 2003).
Strongly defensive when cornered/handled: frequent striking, biting, and vigorous thrashing (Ernst & Ernst, 2003).
Anti-predator displays include body flattening and head/neck enlargement; may mimic cottonmouth posture (Gibbons & Dorcas, 2004).
Releases pungent cloacal musk and feces when disturbed; handling greatly increases defensive behavior (Ernst & Ernst, 2003).
HUB pattern: most individuals are solitary; local crowding occurs at optimal basking sites and winter refugia, varying by habitat and season (Ernst & Ernst, 2003).

Communication

Hissing Forced exhalation) during defensive displays (Ernst & Ernst, 2003
Chemical cues/pheromones used in mate searching and courtship; tongue-flicking samples scent trails Greene, 1997
Tactile courtship contact Male chin-rubbing/aligning with female) consistent with colubrid mating behavior (Greene, 1997
Visual threat signals: coiling, open-mouth gaping, body flattening; may elevate forebody before striking Gibbons & Dorcas, 2004
Chemical defense signaling via cloacal-gland musk and fecal release during harassment Ernst & Ernst, 2003

Habitat

River/Stream Lake Pond Wetland Swamp Marsh Bog Estuary Coastal Deciduous Forest Woodland Grassland Agricultural/Farmland Suburban Urban +9
Biomes:
Freshwater Wetland Temperate Forest Temperate Grassland Boreal Forest (Taiga)
Terrain:
Riverine Coastal Valley Plains Hilly Rocky Sandy Muddy +2
Elevation: Up to 3937 ft

Ecological Role

Mid-level (mesopredator) aquatic-edge predator linking aquatic and terrestrial food webs.

Regulates local populations of small fish and amphibians (predation pressure in freshwater communities). Transfers energy/nutrients between aquatic and terrestrial systems via prey capture in water and digestion/egestion on land or basking sites. Serves as important prey for higher trophic levels (e.g., herons/egrets, hawks, raccoons, otters), supporting wetland and riparian predator communities.

Diet Details

Main Prey:
Fish Amphibians Crayfish Aquatic and semiaquatic vertebrates Aquatic invertebrates

Human Interaction

Domestication Status

Wild

Northern Water Snake (Nerodia sipedon) is wild and not domesticated. People often kill it after mistaking it for a cottonmouth or catch it near freshwater. It is used little in education and research. Nerodia face road deaths, pond conflicts, and a small wild-caught pet trade. They are semi-aquatic, bite strongly, and bear live young.

Danger Level

Low
  • Bites: nonvenomous but defensive; may bite repeatedly when handled. Bites can be painful and can bleed due to numerous small recurved teeth; secondary infection is a risk if wounds are not cleaned.
  • Defensive musk/feces: releases strong-smelling cloacal secretions when threatened; can cause temporary irritation and is unpleasant during handling.
  • Misidentification risk: frequently mistaken for venomous cottonmouths, leading to risky attempted killing/handling by people and increased human-snake conflict.
  • Water-edge encounters: startled individuals may thrash or bite when stepped on or grabbed near shorelines; risk is primarily to hands/forearms during capture/handling.

As a Pet

Not Suitable as Pet

Legality: Laws vary. Many U.S. states allow keeping Northern Water Snake (Nerodia sipedon), but wild collection, permits, transport across state lines, and local rules may limit ownership. Check state and city wildlife laws.

Care Level: Experienced

Purchase Cost: Up to $150
Lifetime Cost: $1,200 - $4,500

Economic Value

Uses:
Ecosystem services Education/outreach Research Wildlife viewing Nuisance/conflict (indirect cost)
Products:
  • Non-consumptive value: predator of fish/amphibians that can influence local aquatic food webs (ecosystem service rather than a commercial product).
  • Occasional use in live educational displays and herpetology research (non-commercial or low commercial value).
  • Indirect economic impacts: can be perceived as a nuisance at private ponds or near fish-stocking operations; costs are typically related to exclusion/relocation rather than damage.

Relationships

Predators 8

Great Blue Heron
Great Blue Heron Ardea herodias
Green Heron
Green Heron Butorides virescens
Bald Eagle
Bald Eagle Haliaeetus leucocephalus
Red-tailed Hawk Buteo jamaicensis
Raccoon
Raccoon Procyon lotor
North American River Otter
North American River Otter Lontra canadensis
Common Snapping Turtle
Common Snapping Turtle Chelydra serpentina
Eastern Kingsnake Lampropeltis getula

Related Species 9

Brown Watersnake
Brown Watersnake Nerodia taxispilota Shared Genus
Diamondback Watersnake Nerodia rhombifer Shared Genus
Banded Watersnake
Banded Watersnake Nerodia fasciata Shared Genus
Plain-bellied Watersnake Nerodia erythrogaster Shared Genus
Green Watersnake Nerodia cyclopion Shared Genus
Gulf Saltmarsh Snake Nerodia clarkii Shared Genus
Eastern Garter Snake Thamnophis sirtalis Shared Family
Queen Snake
Queen Snake Regina septemvittata Shared Family
Northern Red-bellied Snake Storeria occipitomaculata Shared Family

Ecological Equivalents 5

Animals that fill a similar ecological role in their ecosystem

Cottonmouth
Cottonmouth Agkistrodon piscivorus Nerodia sipedon is often found in the same slow waters, swamps, and lake or river edges; it resembles and behaves like a water snake, reaches about 61–107 cm (up to 135 cm), and is frequently mistaken for the venomous cottonmouth.
Diamondback Watersnake Nerodia rhombifer Exhibits a similar semi-aquatic niche, ambushing and actively hunting fish and frogs, and displays the same Nerodia defensive behaviors. It mainly differs by having a more central/southern range and a different body pattern, yet fills the same role where ranges meet.
Brown Watersnake
Brown Watersnake Nerodia taxispilota Ecological counterpart in much of the southeastern U.S.; a large-bodied Nerodia that specializes on fish in rivers, streams, and impoundments. Often basks on overhanging vegetation or structures and retreats to water when disturbed—behaviors broadly shared with Nerodia sipedon.
Banded Watersnake
Banded Watersnake Nerodia fasciata Occupies similar freshwater-edge habitats (marshes, swamps, ponds) and uses a similar prey base (fish and amphibians). Where ranges are near, it serves as a close ecological analog, sharing thermoregulatory behavior (basking) and defensive displays/musking typical of watersnakes (Gibbons & Dorcas, 2004).
Queen Snake
Queen Snake Regina septemvittata Occurs in the same semi-aquatic freshwater streams and rivers as Nerodia sipedon but has a different diet: it mainly eats crayfish (especially newly molted individuals), while Nerodia sipedon eats many fish and amphibians.

The northern water snake is often confused for the venomous cottonmouth and the copperhead, although it is nonvenomous.

The northern water snake is a species of common water snake that is native to North America and found in the eastern and central regions. Related to garter snakes, it is also called a water snake or a common water snake. Along with the banded or southern water snake, it was introduced to California, where it competes with the native giant garter snake.

4 Incredible Northern Water Snake Facts!

  • While it is nonvenomous, it has a nasty bite that releases anticoagulant, which makes the wound bleed a lot.
  • This snake is beneficial to humans because it gets rid of pests such as mice.
  • It only attacks if it is picked up or threatened, but will bite repeatedly until or unless it’s released.
  • The northern water snake first flees into any nearby water when threatened.

The northern water snake flees to water when threatened.

©iStock.com/Doug Gordon

Scientific Name

The scientific name of the northern water snake is Nerodia sipedon. Its genus, Nerodia, contains nonvenomous water snakes. There are nine species in Nerodia and they’re all native to North America.

This species has many common names, including the banded water snake, northern banded water snake, common water snake, water snake, black water adder, black water snake, common northern water snake, northern water snake, North American water snake, brown water snake, water pilot, eastern water snake, spotted water snake, and streaked snake.

The scientific name of the northern water snake is Nerodia sipedon.

©iStock.com/manuellacoste

Evolution and Origins

The northern water snake is in the snake family Colubridae, which has 249 genera and means “snake” in Latin. Fossil records of colubrids date to the Pliocene (Blancan) 5.333 million to 2.58 million years ago.

Scientists believe that the similarity in appearance between the water snake and the venomous cottonmouth might have been an evolutionary adaptation on the part of the water snake so it could avoid or confuse predators.

Northern Water Snake (nerodia sipedon)

The northern water snake’s similarity to the cottonmouth may have been an evolutionary adaptation.

©Steve Byland/Shutterstock.com

4 Types of Northern Water Snake

There are four subspecies of the northern water snake. They are:

  • Northern water snake (Nerodia sipedon sipedon): The nominate subspecies is present across eastern and central North America, with the northern end of the range being southern Ontario and southern Quebec and the southern point of the range Texas and Florida.
  • Lake Erie water snake (Nerodia sipedon insularum): This snake can be found on the rocky shorelines and cliffs of the American and Canadian islands in western Lake Erie.
  • Midland water snake (Nerodia sipedon pleuralis): This subspecies is located in the central and southern United States.
  • Carolina water snake (Nerodia sipedon williamengelsi): This water snake lives in North and South Carolina.

There are four subspecies of the northern water snake.

©iStock.com/IcemanJ

Appearance

Because of its superficial appearance of a medium to large size, thick body, dark blotches, and being aquatic, the northern water snake is often confused for the venomous cottonmouth and the copperhead, although it is nonvenomous. It is also confused for the nonvenomous brown water snake and the banded water snake.

Hence, identification is through physical features and relative size rather than colors. Differentiation from the cottonmouth comes from the northern water snake’s longer, thinner body, flat head as wide as the neck, round pupils, and lack of heat-sensing pits, fangs, and venom glands.

How to identify northern water snakes:

  • A size of up to 4.5 feet in length including the tail, but an average of two feet eight inches for females and two feet 3.5 inches for males
  • A weight of 5.5-14.5 ounces for females and 2.9-5.4 ounces for males
  • Tan, reddish-brown, brown, grey, brownish-black, reddish-purple, or black colors on and up to completely black bodies
  • Brown, reddish-brown, black, or dark green splotches on its body
  • Dark crossbands on the neck
  • Cream, yellow, or gray belly with black and reddish half-moon spots in various patterns
  • Baby snakes are lighter in color than adults.
Nothern water snake in leaves- Brown snakes in Ohio

The northern water snake has brown, reddish-brown, black, or dark green splotches on its body.

©Steve Byland/Shutterstock.com

Behavior

During the winter, northern water snakes go into hibernation. People often find them sunbathing on rocks, tree stumps, and brush during the warmer months. They are active both during the day and at night. It does not seek confrontation with people and other animals but will aggressively bite if threatened or handled. Some people enjoy these snakes for being a form of biological pest control.

Snakes That Look Like Copperheads-Northern Water Snake

The northern water snake often sunbathes on rocks during the warmer months.

©jmarino/Shutterstock.com

Venom: How Dangerous Are Northern Water Snakes?

These snakes do not go after humans and attack them unless they are threatened or handled. They are neither poisonous nor venomous, but the facts about them show that they release a strong-smelling musk and have powerful jaws that can give harsh bites over and over. It also releases an anticoagulant that makes the wound bleed a lot. If you are bitten by one, treat the wound and seek medical attention if the bite is severe or develops an infection.

Snakes in Maine - Northern Water Snake / Lake Erie Watersnake (Nerodia sipedon insularum)

The northern water snake is not venomous.

©Michiel de Wit/Shutterstock.com

Habitat

The northern water snake’s range is in eastern and central North America. These snakes are especially plentiful in southeast Canada and the northeastern United States. Making their habitat on riverbanks and near lakes, they use beaver and muskrat dens for shelter. They come out after their winter hibernation, where they socialize during the spring and fall and are solitary during the summer. The mating season is from April through June.

Nerodia sipedon

Northern water snakes socialize during the spring and fall.

©samray/Shutterstock.com

Diet

Northern water snakes are carnivorous and their diet consists of fish, amphibians such as frogs, smaller or baby reptiles, rodents, small mammals, and invertebrates.

They are ambush predators. During the day they hunt along the water’s edge in plants, and at night they hunt small fish sleeping in shallow water.

American Green Tree Frog

Frogs are part of the northern water snake’s diet.

©LorraineHudgins/Shutterstock.com

Predators and Threats

Baby snakes are particularly vulnerable to being prey and having short lifespans if they are eaten, but their lifespan in the wild is unknown. Their predators are larger snakes, snapping turtles, raccoons, opossums, and foxes.

The northern water snake is vulnerable to predators when young.

©Tucker Heptinstall/Shutterstock.com

Population and Conservation

According to the IUCN, the northern water snake population is stable and listed as Least Concern. The Lake Erie watersnake subspecies was threatened in 1999 due to being killed by humans, habitat loss, and degradation. However, the invasive species of the round goby was introduced, becoming up to 90% of its diet, and the snake recovered enough to where the United States Fish and Wildlife Service removed its threatened status in 2011.

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Sources

  1. Wikipedia / Accessed January 26, 2022
  2. Snake Removal / Accessed January 26, 2022
  3. New Jersey Division of Fish and Wildlife / Accessed January 26, 2022
  4. Lake Eerie Watersnake / Accessed January 26, 2022
  5. Chester County Parks + Preservation / Accessed January 26, 2022
  6. Untamed Science / Accessed January 26, 2022
  7. Snakes for Pets / Accessed January 26, 2022
Catherine Gin

About the Author

Catherine Gin

Catherine Gin has more than 15 years of experience working as an editor for digital, print and social media. She grew up in Australia with an alphabet of interesting animals, from echidnas and funnel-web spiders to kookaburras and quokkas, as well as beautiful native plants including bottlebrushes and gum trees. Being based in the U.S. for a decade has expanded Catherine's knowledge of flora and fauna, and she and her husband hope to have a hobby farm and vegetable garden in future.

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Northern Water Snake FAQs (Frequently Asked Questions)

When separating northern water snakes vs cottonmouths, you can focus on their appearance. While both snakes are similar in length, cottonmouths are more banded while northern water snakes have blotches. In addition, the pupils of cottonmouth eyes are elliptical, whereas northern water snakes have round pupils.

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