A snake found near water can cause alarm, but most aquatic species in North America are harmless, non-venomous members of the Nerodia genus, commonly called water snakes. These snakes are highly abundant in various aquatic habitats, including slow-moving rivers, lakes, marshes, and ponds. Accurate identification is important for human safety and for conservation, as they are often mistakenly killed out of fear.
Visual Keys for Non-Venomous Water Snakes
Water snakes (Nerodia genus) share physical traits that distinguish them from other species. Their scales are heavily keeled, meaning each scale has a ridge running down the center, giving the snake a rough, textured appearance rather than a smooth one. This roughness is most noticeable when the snake is dry and basking.
The head is generally narrow and elongated, blending into the neck without the abrupt, triangular shape seen in some venomous snakes. They have round pupils, characteristic of non-venomous species. Water snakes have relatively thick bodies, which contributes to their frequent misidentification, but their thickness often tapers sharply toward the tail.
Coloration is variable, ranging from brown, tan, or gray, often featuring bands, blotches, or diamond-shaped patterns. As water snakes age, their skin tends to darken, sometimes appearing nearly solid brown or black, obscuring younger patterns. This darkening makes older specimens difficult to identify and frequently confused with other dark, heavy-bodied snakes.
The Critical Difference: Water Snakes Versus Cottonmouths
Distinguishing a water snake from the venomous Cottonmouth (Agkistrodon piscivorus), also known as the Water Moccasin, is the most important distinction for safety. The Cottonmouth is a pit viper, possessing a deep, heat-sensing pit between its eye and nostril, a feature absent on water snakes. This status gives the Cottonmouth a broad, spade-shaped head that is noticeably wider than its neck due to large venom glands.
In contrast, the water snake’s head is more streamlined and its neck is not distinctively narrower than its body. The Cottonmouth also features vertically elliptical, or cat-like, pupils, whereas the water snake has round pupils. Furthermore, the Cottonmouth’s eyes are partially obscured by scales and are not easily visible when viewed from directly above, unlike the water snake’s eyes.
A significant behavioral difference is observed when the snakes are swimming. Non-venomous water snakes typically swim with most of their body submerged beneath the water’s surface, with only their head and a small portion of their back visible. The Cottonmouth, however, is often buoyant and tends to swim with its entire body floating on top of the water, a distinctive surface-skimming behavior. When threatened, the Cottonmouth is known for its defensive display of “gaping,” where it opens its mouth wide to expose the bright white lining.
Understanding Defensive Behavior and Safe Encounters
When a water snake feels threatened, its first reaction is usually to flee quickly toward the safety of the water or nearby cover. If escape is not possible, the snake will resort to a common defensive posture: flattening its body and head. This flattening action makes the head appear much wider and more triangular, effectively mimicking the appearance of a venomous snake and contributing to misidentification.
If handled or cornered, water snakes will strike repeatedly and bite vigorously, a behavior that leads to their reputation for aggression. While their bite is not venomous, it can result in minor lacerations which should be thoroughly cleaned to prevent infection, as bacteria can inhabit the snake’s mouth. Another defense mechanism involves expelling a foul-smelling, musky substance from their cloaca when disturbed, an odor meant to deter predators.
The safest protocol when encountering any snake near the water is to maintain a respectful distance and observe it without intervention. Never attempt to handle, capture, or kill a snake, as this is when bites most frequently occur. Giving the animal space allows it to retreat naturally and eliminates the risk of a defensive reaction.