Cottonmouth (Water Moccasin) in Tennessee: Complete Identification Guide

The cottonmouth — also called the water moccasin — is one of the most misidentified snakes in Tennessee. It shares its habitat with several harmless water snakes that look remarkably similar, and the consequences of misidentifying one in either direction can be serious.

This guide covers everything you need to know: how to identify a cottonmouth, where to find them in Middle Tennessee, how to tell them from lookalikes, and what to do if you encounter one.

The western cottonmouth (Agkistrodon piscivorus leucostoma) is the only venomous water snake in North America. It is a pit viper — the same family as copperheads and rattlesnakes — and shares the characteristic broad, triangular head and heat-sensing pit organs of that group.

The name "cottonmouth" comes from the snake's defensive display: when threatened, it opens its mouth wide to reveal the bright white interior lining. This gaping display is a warning, not an attack posture.

Size: Adult cottonmouths typically range from 24 to 48 inches. Large individuals can reach 5 feet, though this is uncommon. They are heavy-bodied snakes — significantly thicker in proportion to their length than most harmless water snakes.

Color and Pattern: Cottonmouth coloration varies considerably with age and individual variation:

• Juveniles: Strongly patterned with dark brown crossbands on a lighter background, with a bright yellow tail tip (used to lure prey). Juveniles are frequently mistaken for copperheads.
• Adults: Pattern often fades with age. Many adult cottonmouths are uniformly dark brown, olive, or nearly black with little visible banding. Some retain a faint banded pattern visible in certain lighting.

Head: Broad and triangular, distinctly wider than the neck. The head is large relative to body size — noticeably more massive than the heads of harmless water snakes. Heat-sensing pit organs are visible between the eye and nostril on each side.

Eyes: Elliptical (cat-like) pupils, visible at close range. Harmless water snakes have round pupils.

Belly: The belly is typically pale with dark mottling or blotching.

The white mouth: The bright white interior of the mouth is the most distinctive feature when the snake is displaying defensively. No harmless Tennessee snake has this combination of white mouth lining and heavy, dark body.

Cottonmouths are semi-aquatic and are almost always found near water. In Middle Tennessee, look for them:

Along creek and river corridors. The Cumberland River, Harpeth River, Stones River, and their tributaries all support cottonmouth populations. Cottonmouths are common along the wooded banks of these waterways.

Around lakes and reservoirs. Percy Priest Lake, Old Hickory Lake, J. Percy Priest, and other impoundments in the region have cottonmouth populations, particularly in coves and along wooded shorelines.

In wetlands, swamps, and drainage ditches. Any low-lying, wet area with vegetation can harbor cottonmouths. This includes drainage ditches, retention ponds, and flooded fields.

Basking sites near water. Cottonmouths are frequently seen basking on logs, rocks, and banks at the water's edge. They are less likely to flee quickly than most snakes — they tend to hold their ground and display rather than retreat.

In residential areas near water. Homeowners with properties adjacent to creeks, ponds, or lake edges in Davidson, Williamson, Sumner, and Wilson counties regularly encounter cottonmouths.

The northern water snake (Nerodia sipedon) is the snake most commonly mistaken for a cottonmouth in Tennessee. This is an important distinction because northern water snakes are completely harmless — but they are aggressive biters when handled, which reinforces the mistaken belief that they are venomous.

Here is how to tell them apart:

Cottonmouth: Broad, triangular, distinctly wider than the neck. The head looks almost too large for the body. Water snake: Narrower, more oval-shaped, blending more smoothly into the neck. Still somewhat broad, but noticeably less so than a cottonmouth.

Important caveat: Northern water snakes flatten and widen their heads dramatically when threatened, mimicking the triangular shape of a viper. Do not rely on head shape alone when the snake is in a defensive posture.

Cottonmouth: Elliptical (vertical slit), like a cat's eye. Water snake: Round.

This is one of the most reliable distinguishing features — but it requires getting close enough to see the eyes clearly, which is not always safe or practical.

Cottonmouth: Very heavy-bodied. The body is thick and robust throughout its length. Water snake: Moderately heavy-bodied but noticeably slimmer than a cottonmouth of similar length.

Cottonmouth: Neck is very narrow relative to the wide head, creating a pronounced "neck" behind the head. Water snake: The transition from head to neck is less dramatic.

Cottonmouth: Swims with most of its body on the surface of the water, body inflated with air. The head is held up and out of the water. Water snake: Swims with most of its body submerged, only the head above water.

This is one of the most reliable field identification features and can be observed from a safe distance.

Cottonmouth: Tends to hold its ground when approached. Will coil, gape (open mouth to show white interior), and vibrate its tail. Rarely retreats quickly. Water snake: More likely to flee into the water when approached. When cornered, will flatten its body, bite aggressively, and release musk — but does not gape to show a white mouth.

Banded Water Snake (Nerodia fasciata): Found in western Tennessee but less common in Middle Tennessee. Similar banded pattern to juvenile cottonmouths. Non-venomous.

Diamondback Water Snake (Nerodia rhombifer): Found in western Tennessee. Heavy-bodied with a distinctive chain-link pattern. Non-venomous but frequently mistaken for a cottonmouth.

Juvenile Copperhead: Young cottonmouths and young copperheads look similar — both have banded patterns and yellow tail tips. The key difference is habitat: copperheads are terrestrial and found in wooded upland areas; juvenile cottonmouths are found near water.

They do not chase people. This is one of the most persistent myths about cottonmouths. They do not pursue humans. If a cottonmouth appears to be moving toward you, it is almost certainly moving toward water — which happens to be in your direction.

They are more defensive than aggressive. The gaping display is a warning, not a prelude to attack. A cottonmouth that is gaping at you is telling you to back off. If you do, it will almost always stand down.

They are most active at night in summer. Like many pit vipers, cottonmouths are more active after dark during hot weather. Night fishing, night swimming, and walking near water after dark in cottonmouth territory carries elevated risk.

They can bite underwater. Unlike most snakes, cottonmouths can open their mouths and bite while submerged. This is relevant for anyone wading in areas where cottonmouths are present.

They do not always rattle before striking. Unlike rattlesnakes, cottonmouths have no rattle. The gaping display is their primary warning behavior, but a startled cottonmouth may strike without warning.

Cottonmouth venom is hemotoxic — it destroys blood cells and tissue. Bites cause significant local tissue damage, pain, and swelling. Severe bites can cause permanent tissue loss.

Cottonmouth venom is more potent than copperhead venom and causes more severe local effects. However, cottonmouths inject less venom per bite on average than timber rattlesnakes. All cottonmouth bites require emergency medical evaluation.

If bitten:

1. Call 911 or get to an emergency room immediately
2. Keep the victim calm and still
3. Remove rings, watches, and tight clothing from the affected limb
4. Do not cut the wound, apply a tourniquet, or attempt to suck out venom
5. Note the time of the bite

CroFab antivenom is effective against cottonmouth venom and is available at major Nashville-area hospitals.

Near water on a trail or in the wild: Give it a wide berth. Move away slowly and let it be. Cottonmouths near water are in their natural habitat and pose no threat if left alone.

On your property: Do not approach, handle, or attempt to kill it. Call Nashville Snake Removal at (615) 613-5992. We handle cottonmouth removal throughout Middle Tennessee, including properties adjacent to Percy Priest Lake, Old Hickory Lake, and creek corridors throughout Davidson, Williamson, Sumner, and Wilson counties.

If you are unsure whether it is a cottonmouth: Call our 24-hour identification hotline. Describe what you are seeing or send a photo, and we will tell you exactly what you are dealing with.

If your property borders water in Middle Tennessee, cottonmouth encounters are a realistic possibility. These steps reduce the risk:

• Keep grass and vegetation mowed near the water's edge. Dense vegetation provides cover and makes snakes harder to see.
• Avoid reaching into brush or vegetation near water without looking first. Most bites happen when someone reaches into an area without checking.
• Wear boots when walking near water in snake season (April–October). Leather boots provide meaningful protection against bites to the foot and ankle.
• Use a flashlight near water at night. Cottonmouths are more active after dark in summer.
• Teach children not to handle any snake near water. Even if a child is confident it is a water snake, the risk of misidentification is too high.

Nashville Snake Removal serves Davidson, Williamson, Sumner, Wilson, Robertson, Dickson, and Stewart counties. Same-day service available. Call (615) 613-5992.