Their range extends along the brackish salt marshes of the Gulf of Mexico and the Atlantic Coast from Texas to Florida, with an additional population in northern Cuba.

Its scaly reptilian skin acts as a barrier against external dehydration, but, if ingested, seawater draws the less-salty fluid from blood and tissues into the stomach.

N. clarkii is the only species to establish itself in this saline niche, drinking only rainwater when it is available, and at other times swallowing nothing but prey animals with the same diluted body fluids as their own.

[8] All water species of snake (including N. clarkii) are typically considered to be non-venomous, though they do employ a complex series of enzymes in their saliva, resulting in some inflammation and edema to those who have been bitten.

The belly is reversed in color from the dorsum, and is reddish with a central light line of cream-colored oval blotches, often flanked by a row of pale spots.

[8] Members of this race are primarily nocturnal during hot summer nights, but may be found basking and foraging during daylight hours in cool weather.

[9] The mangrove salt marsh snake's native range of populations is in Florida, from Tampa Bay south to Miami and northward along the Atlantic coast to the vicinity of Cape Canaveral.

Within this range, N. c. compressicauda primarily inhabits inundated estuary forests of buttonwood and red mangroves, so as to minimize competition with Florida's numerous freshwater natricines.

[8] This subspecies exhibits many colors and patterns and can be gray, green, or tan with darker banding or may even be solid reddish orange or straw yellow.

[10] A third subspecies, the Atlantic salt marsh snake (N. c. taeniata), in its pure form is restricted to a small stretch of coastline in Volusia and Indian River Counties, Florida.