This is a medium to large-sized semi-aquatic snake characterized by its robust, cylindrical body. Adults typically measure between 50 and 90 centimeters (20 to 35 inches) in length, with adult females frequently reaching or exceeding 100 centimeters (39 inches). Its dorsal scales are strongly keeled, giving the body a highly textured, rough appearance. The dorsal coloration is predominantly inconspicuous, varying from olive-brown to dark gray or blackish, often accompanied by faint, dark longitudinal bands. Conversely, its most striking and diagnostic feature is located on its ventral side, which presents a vivid pattern consisting of three distinct longitudinal black stripes set against a vibrant background of yellow, orange, or bright red. The eyes and nostrils are positioned dorsally on the head, an evolutionary adaptation that allows the snake to navigate, breathe, and hunt while remaining almost entirely submerged.

Geographical distribution: It is widely distributed across the temperate and subtropical regions of central-southern South America. Its geographic range encompasses southern Brazil (including the states of Rio Grande do Sul, Santa Catarina, Paraná, and São Paulo), the entirety of Uruguay, eastern Paraguay, and the northeastern provinces of Argentina (such as Misiones, Corrientes, Entre Ríos, Santa Fe, Chaco, and Formosa). This distribution pattern is closely tied to the extensive river basins of the region, particularly those of the Paraná, Uruguay, and Paraguay rivers.

Habitat: This species is strictly associated with freshwater aquatic ecosystems with slow-moving or stagnant waters. It is commonly found in swamps, marshes, permanent lagoons, slow-flowing streams, and temporarily flooded grasslands. Furthermore, it displays significant ecological resilience, frequently inhabiting human-modified landscapes such as irrigation canals, drainage ditches, and flooded rice fields, where the high concentration of prey items supports dense populations.

Feeding: It has a carnivorous diet specialized in aquatic prey. Its primary food sources consist of teleost fish of various sizes and a wide range of amphibians, including both larval tadpoles and adult frogs and toads. The species is an active underwater hunter, utilizing visual cues and chemical signals processed through its Jacobson´s organ to locate prey. Its saliva contains mild toxins produced by the Duvernoy´s gland, which help immobilize struggling prey before they are swallowed whole under the water or on nearby muddy banks.

Behavior: Its activity patterns range from diurnal to crepuscular, although it may exhibit increased nocturnal activity during the hottest periods of the summer. As an exceptional swimmer and diver, it can remain submerged for substantial periods. When threatened, its primary defense mechanism is to flee rapidly toward deep water. However, if cornered, it displays defensive behaviors such as flattening its body dorsoventrally to appear larger, producing loud hisses, and releasing a foul-smelling cloacal secretion. Despite these intimidating displays and potential defensive strikes, it possesses no functional venom delivery system dangerous to humans, making it completely harmless to people.

Reproduction: This species is viviparous, giving birth to live young rather than laying eggs, which is a highly successful adaptation for animals living in flood-prone environments. The reproductive cycle is seasonal, with mating typically occurring during the spring. After a gestation period lasting several months, females give birth to a litter of 10 to 30 fully formed young during the late summer or early autumn. Neonates measure approximately 15 to 20 centimeters (6 to 8 inches) at birth and quickly become independent, beginning to feed on small tadpoles and aquatic insects shortly after birth.

Conservation status: It is currently classified as Least Concern (LC) on the IUCN Red List, owing to its extensive distribution range, large population sizes, and capability to adapt to anthropic wetlands. Nonetheless, local populations face significant threats from habitat destruction, drainage of wetlands for agricultural expansion, water pollution due to pesticides, and direct eradication by humans who frequently mistake this harmless species for venomous pit vipers belonging to the genus Bothrops.