Northern water snake size explained: Why this harmless snake can look massive

Northern water snakes are some of the most common snakes found around ponds, rivers, swamps, and lakes in eastern parts of America and Canada. They are also among the most misunderstood snakes. For starters, many people describe northern water snakes as unusually large snakes when they spot them next to the water bodies. The truth is that these snakes are harmless because they are not venomous. There are many biological and optical reasons for them appearing to be unusually large.

According to wildlife biologists, the reason behind the misconception is due to body shape, swimming posture, lighting, and environments where these snakes exist. It is their physical structure that makes them appear bigger than they look like.

Actual size of northern water snakes


Northern water snakes are medium to large-sized snakes according to North American standards. As explained on the Savannah River Ecology Laboratory website from the University of Georgia, adults normally grow from 24 to 55 inches in length. These sizes are quite large for any snake. Compared to other thin-bodied snakes, northern water snakes have thick bodies.

When scientists investigated Lake Erie water snakes, a group of northern water snakes, they noticed that females could reach a bigger body size than males. One of the studies posted at PubMed revealed that females' body sizes were much greater than those of males from the same population.

This explains why in some cases, the snake is spotted looking unusually big. A mature female lying across a bank of a river looks much bigger than an ordinary adult snake. Scientists studying populations of northern water snakes noted that body size variation is common in this species. They claim that many individuals do not realize how big a water snake can get to be.

Why does a snake look bigger in water?

When an individual is in water, the size is perceived differently. This is one of the main reasons why northern water snakes look so large. The biomechanics research published in PubMed found out that when northern water snakes move fast in the water, some parts of their bodies become temporarily compressed.

It should be noted that snakes do not grow bigger while moving. What actually happens is that there is a change in the shape of the body in such a way that it becomes thicker and heavier when viewed from above. Reflections, ripples, and angle of view contribute to the appearance. These snakes are typically observed from afar over ponds and rivers as opposed to clear visibility.

This effect can also happen due to biomechanics, according to which water-distorted snakes could be perceived by humans differently. It means that a snake swimming near the surface will appear longer and fatter in comparison to snakes that are on land.

Why northern water snakes appear more dangerous

Habitat can influence reactions toward the species. Northern water snakes are usually found in areas where people are cautious, such as muddy riverbanks, marshes, docks, and overhanging tree branches. In addition, according to Connecticut Department of Energy & Environmental Protection, the appearance of northern water snakes often makes them confused with dangerous species because of their dark coloration and stocky bodies.

If these snakes bask on a log or branch, their bodies are visible from almost all sides, making them appear extra big. The snake is also known to be aggressive and show defensive behavior when it feels under attack.

According to guidance about wild animals in Massachusetts, northern water snakes have been reported to flatten themselves out, excrete musk, and bite multiple times when trapped. Such defensive measures tend to fuel the misconception that this nonvenomous snake is highly dangerous.

Why people mistake them for venomous snakes

Northern water snakes are regularly mistaken for venomous snakes, including cottonmouths and copperheads. It seems that this misconception arises because of a number of similar characteristics that the species possesses compared to venomous snakes. According to the wildlife identification guide provided by Clemson University, the species is among the ones that are frequently mistaken for copperheads.

Moreover, the snake is known for its stout body, dark bands, and damp appearance, which makes people afraid almost immediately, especially when spotted around water. Massachusetts wildlife officials also note that people often think that the snake is a cottonmouth, although cottonmouths are not found in this region at all.

Scientific information about the appearance of the snake

According to scientists, the northern water snake is an excellent illustration of how appearances of wildlife can affect people's views on the issue. Firstly, the species is actually large compared to other backyard snakes. The most notable specimen in this regard are adult females. Second, water distortions, defense mechanisms, and habitat make this animal seem more dangerous than it really is.

Consequently, there is a harmless native snake that enjoys a rather terrifying reputation. The reason why wildlife professionals advise people not to hurt these animals is that they represent an important part of freshwater systems thanks to eating fish, amphibians, and small aquatic prey.

From a layman's point of view, the bottom line is that northern water snakes may seem dramatic but not as much as they appear due to their environment and people's reaction to them.