The distribution of water snakes in the USA is illustrated in the table below. You can download a pdf of the table here.
The green water snake Nerodia cyclopion is a relatively large snake with a greenish gray or olive brown color on its dorsal side. It is considered highly aquatic in the sense that it spends more time in the water than most other water snake species.
However, on rainy days it can be found up to 100 meters away from water. When captured the green snake will bite and secrete a musk, which smells worse than the musk from other water snakes. The difference between sexes of the green water snake is evident. The female is approximately 25% larger than the male (Fitch, 1981) 1.
Note: In Vermont, New York, South Dakota, Minnesota, Nevada, New Jersey, New Hampshire, South Dakota, Nebraska, Colorado, Connecticut, Montana, Massachusetts, Vermont, Pennsylvania, Maine, Wisconsin, Rhode Island, West Virginia, Rhode Island, and Colorado only the Northern water snake is found.
Water snakes are not found in Alaska, Oregon, Washington, Idaho, Utah, Wyoming, Hawaii, North Dakota, and Arizona.
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The salt marsh snake (Nerodia clarkii) is the smallest of the water snakes in the United States, and it is the only water snake that prefers salt water or brackish water. It reaches a length of one meter, and the salt marsh snake is distinguished from all other water snakes by its unusual tail: a compressed section and lack of a round shape like most other water snakes. However, this can be difficult for non experts to see. Salt marsh snakes can be found along the coast from Texas to Florida.
As this snake is perhaps the most common snake in the U.S., it is described at the index page of this website.
The plain-bellied water snake (Nerodia erythrogaster) is distinguished from other water snakes by the uniform color on its ventral scales (on its belly/underside) without any spotting. The eyes of the plain-bellied water snake are larger than those of other water snakes. Plain-bellied water snakes are particularly abundant in temporary wetlands, possibly because the snakes seem to have a preference for the amphibians that dwell there.
Male banded water snakes (Banded Water Snakes: Nerodia fasciata) usually reach a length of three feet, while females grow a bit longer. Banded water snakes have cross bands down the entire length of the body. They are generalist with respect to habitat and can be found in almost any type of freshwater habitat. In places where both the banded water snake and the Northern water snake are present, the two species segregate. The banded water snakes confine themselves to ponds and lakes while the Northern water snake confines itself to habitats with streaming water.
The Brazos water snake (Nerodia harteri harteri) is a fast-moving, relatively slender and small snake. Its color varies from brown to grayish brown, and it has four lengthwise rows of four olive brown spots. This snake, normally reaching lengths of two feet, is only found in central Texas, where it lives near fast-flowing, shallow areas of the Brazos River. It prefers water less than one foot deep and a river floor with stones so it can find plenty of small fish. It is not as vicious as other water snakes, and its teeth are too short to penetrate the skin of an adult 2.
Like the Brazos water snake, the Concho water snake (Nerodia harteri paucimaculata) is a small slender snake rarely exceeding three feet in length. It has four rows of alternating blotches on its back. It is usually found in the same places as the diamondback water snake and the blotched water snake and can be distinguished from those by its smaller size. The Concho water snake is endemic to Texas and can be found along the Concho River. It prefers free flowing areas of the lake. On hot summer days, juvenile Concho water snakes are often found beneath rocks, and on such days, they are mainly active during the morning. This snake's diet mainly consists of fish.
The diamonback water snake (Nerodia rhombifer) is a large and heavy snake reaching a length of four feet, although larger specimens have been reported.
The blotched water snake is actually a subspecies of the plain-bellied water snake with the Latin name Nerodia erythrogaster transversa and it is not described in detail here (not yet).
The brown water snake (Nerodia taxispilota) is a fairly large snake, with adults reaching lengths of 4½ feet. Some people are convinced that this is venomous snake due to its size, but as with all other water snakes, the brown water snake has no poison and is not venomous. This fear is fuelled when these snakes accidentally drop into someone's boat; they instinctively think to get rid of it due to suspicion that they are venomous cottonmouth snakes due to their similar appearance. Chances are that if a snake drops into your boat, it is a water snake, and looking at the abundance of water snakes versus cottonmouths, water snakes are many, many times more common than cottonmouth snakes.
Brown water snakes prefer large rivers and lakes. They typically bask on limbs overhanging the water at heights up to 10-15 feet and drop into the water when disturbed. When disturbed at other places, they flee as well and dive under water. Cottonmouth snakes are almost never found in trees overhanging water.
The Eastern green water snake (Nerodia floridana) is a heavy-bodied snake with either a greyish/greenish or red-brown color above the tail and a yellowed belly. Other names of this species include the Florida water snake and the Congo water snake. To discriminate it from the green water snake or Western green water snake, the name Eastern green water snake seems very logical. They have fairly long teeth and are considered quite obnoxious.
1 Fitch, H.S., Sexual size differences in reptiles, Univ. Kans. Mus. Nat. Hist. Misc. Publ. 70 pp. 1-72 (1981).
2 Werler, J.E., Dixon, J.R., Texas Snakes (2000).