Water snakes are common sights near North American waterways, often leading to confusion and fear among people enjoying the outdoors. Due to their preference for aquatic habitats, these snakes are frequently misidentified as the highly venomous Cottonmouth (Water Moccasin). This widespread fear has led to the unnecessary killing of countless non-venomous snakes every year. Understanding the true nature of water snakes is the first step toward safe coexistence and appreciating their role in the ecosystem.
Defining Non-Venomous Water Snakes
The majority of snakes referred to as water snakes in North America belong to the genus Nerodia, which includes species like the Northern Water Snake (Nerodia sipedon) and the Banded Water Snake (Nerodia fasciata). These snakes are classified as non-venomous Colubrids, meaning they do not produce venom that is medically significant or dangerous to humans. They are semi-aquatic reptiles, spending most of their time near freshwater sources such as ponds, rivers, and marshes. Their diet consists primarily of fish and amphibians, which they are adept at catching in the water.
While they lack dangerous venom, a defensive bite from a Nerodia species is still possible if the snake feels threatened or is handled. Their teeth are small, but they will readily strike if cornered. Their mouth may contain bacteria, necessitating proper cleaning of any wound. These snakes are heavy-bodied, with strongly keeled (ridged) scales, and give birth to live young.
How to Distinguish Water Snakes from Venomous Look-Alikes
The primary venomous snake mistaken for Nerodia is the Cottonmouth (Agkistrodon piscivorus), a pit viper restricted to the southeastern United States. Head shape provides a reliable initial distinction. Non-venomous water snakes have a slender head that blends smoothly into the neck, while the Cottonmouth possesses a thick, triangular head distinctly wider than its neck.
Another differentiating feature is the eye’s appearance. Nerodia species have round pupils, similar to humans, while the venomous Cottonmouth has vertical, elliptical pupils. Cottonmouths also have facial pits—heat-sensing organs located between the eye and the nostril—which are absent on the non-venomous water snake. When viewed in the water, Nerodia snakes typically swim with their entire body submerged, leaving only their head above the surface. The heavy-bodied Cottonmouth often floats high on the water, with much of its body visible.
Understanding Water Snake Behavior and Temperament
Non-venomous water snakes are defensive animals, not aggressive, and their first instinct when encountered is generally to flee into the water. If escape is not possible, they engage in a defensive display to deter a perceived threat. This behavior often involves flattening their body and head, making them appear larger and more intimidating, leading to their frequent misidentification as the blocky-headed Cottonmouth.
If the threat persists, a Nerodia snake will strike and may bite repeatedly. They also release a foul-smelling, musky secretion from their cloaca as a final deterrent. This combination of head-flattening, striking, and musking makes them seem aggressive, but these actions are purely defensive responses to being handled, cornered, or surprised. The snakes are trying to protect themselves from what they perceive as a predator.
Safe Practices During an Encounter
Encountering any snake near water requires a cautious and respectful approach to ensure safety for both the human and the reptile. The most important rule is to maintain distance and leave the animal completely alone. Never attempt to handle, harass, or kill a snake, as the vast majority of bites occur when a person tries to interact with the animal. Snakes will generally move away on their own if given space.
If a snake bite occurs, whether from a non-venomous or potentially venomous species, immediate action is necessary. Move away from the snake, remain calm, and call for emergency medical assistance. The wound should be cleaned gently with soap and water. Avoid common but dangerous first aid myths, such as applying a tourniquet, cutting the wound, or attempting to suck out venom. If a venomous snake is confirmed in a highly populated area, local animal control or wildlife authorities should be contacted for professional removal.