Harmless · Native to the United States

Diamondback water snake

Nerodia rhombifer (Hallowell, 1852)

Also called diamond-backed watersnake, fish snake
Data updated October 2026

Diamondback water snake basking on a branch over water, showing a dark chainlike pattern with light diamonds
Fig. 1 — Adult basking above a slough. The dark brown chain pattern leaves a row of light diamond shapes along the back.
Close view of a diamondback water snake's head with round pupils and no facial pit
Fig. 2 — Round pupils and no heat-sensing pit separate it from the cottonmouth.

At a glance

The largest, heaviest water snake across much of the Mississippi Valley and southern plains. A dark chain pattern with light diamonds runs down its back. It is harmless, though it bites and musks freely when handled, and it is often killed by people who think it is a cottonmouth.

01

Identification

This is a big, heavy-bodied snake with keeled scales that feel rough. The background color is gray, light brown or dull yellow. Dark brown blotches connect to form a chainlike net down the back, and the spaces between them make light, diamond-shaped patches, which give the snake its name. The belly is yellow with irregular rows of dark spots or half-moons. Adult males have small bumps under the chin, and young snakes are boldly patterned, with an orange belly.

  1. 01Chain pattern with light diamonds. Dark brown blotches linked into a net, leaving a row of pale diamonds along the spine.
  2. 02Yellow belly with dark half-moons. Irregular rows of dark spots or crescent marks on a yellow underside.
  3. 03Round pupils, no facial pit. Its eyes are visible from above, unlike the cottonmouth’s, which sit under a heavy brow.

Commonly confused with

Cottonmouths are dark brown or black without a chain pattern and have a facial pit, vertical pupils and a pale line from the eye to the corner of the mouth. Never handle a snake you cannot identify.

02

Size

01 ft2 ft3 ft4 ft Typical adult · about 40 in (102 cm)

Most adults are 30 to 48 inches (76–122 cm) long, and big females can be very thick-bodied. The Missouri Department of Conservation gives an occasional maximum of 69 inches (175 cm). Louisiana lists a size range of about 18 to 65 inches, which includes young snakes.

03

Range & habitat

Oxbow lake with cypress trees and overhanging willow branches
Fig. 3 — Oxbow lakes, sloughs and swamps of big-river floodplains are typical habitat.

Diamondback water snakes live in the central and south-central United States, from the Mississippi River valley in southern Illinois, Missouri and western Tennessee south to the Gulf Coast, and west through Kansas, Oklahoma and Texas into northeastern Mexico. They are found across Louisiana except in coastal brackish and salt marshes. They favor slow or still water: swamps, sloughs, oxbow lakes, marshes, ponds, drainage ditches and the backwaters of large rivers, including bottomland prairie wetlands in the north of the range.

State guides: Texas · Oklahoma

04

Diet & predators

Diamondback water snakes are fish specialists. They catch mostly small, slow-moving or dead fish, and adults in Louisiana eat a lot of catfish. Frogs, tadpoles, toads and salamanders are the other main prey. Now and then they take crayfish, small turtles or snakes, earthworms, leeches and insects. They do not constrict; they seize prey in the jaws and swallow it.

Feeds on

  • Small and slow-moving fish, including catfish
  • Frogs and tadpoles
  • Toads and salamanders
  • Crayfish and other invertebrates

Preyed on by

  • Herons and other large birds
  • Raccoons and other predatory mammals
  • Other snakes (newborns)
  • Large frogs and fish (newborns)
Frog at the edge of a pond
Prey — frogs.
Great blue heron hunting in shallow water
Predator — large wading birds.

05

Behavior & seasons

Diamondback water snakes are active from about late March through October. In spring and fall they bask on branches, logs, roots and banks, often on shrubs overhanging the water, and drop in when approached. In the heat of July through September they switch largely to night activity. They can stay underwater for more than an hour.

They spend the winter below the frost line in animal and crayfish burrows and old root holes. When cornered, a diamondback water snake flattens its head and neck, strikes and bites, and smears foul musk if picked up. In spring several may gather along a shoreline, a sight sometimes mistaken for a nest of water moccasins.

06

Reproduction

Courtship and mating take place in April and early May. Males rub the bumps on their chins along a female’s back during courtship. Females give birth to live young from late August into early October. Litters are often large, from about 6 to 62. Young reach maturity at about 2.5 to 3 years old.

07

Conservation

The diamondback water snake is not federally listed. It is common across most of its range: Louisiana considers its populations stable, and it is very common in northern and western Missouri. It is not protected in Tennessee. Wetland drainage and road mortality reduce local numbers, and many are killed after being mistaken for cottonmouths.

Keep reading

Sources

Data updated October 2026 · How we build these pages