Is a medium-sized, highly specialized aquatic colubrid reptile whose adult length typically ranges from 70 to 90 centimeters, though exceptionally large females can exceed one meter. Its head is moderately distinct from the neck, featuring dorsally positioned eyes and nostrils, a key morphological adaptation that allows the animal to breathe and scan its surroundings while remaining almost entirely submerged. The dorsal coloration consists of an olive-green, grayish, or yellowish-brown background adorned with conspicuous, alternating dark circular spots that mimic a leopard-like pattern. Ventrally, it exhibits a striking, highly diagnostic checkered pattern of intense red, orange, and black blotches. Its dorsal scales are strongly keeled, giving the skin a rough texture that helps reduce slippage in wet environments and aids in underwater propulsion.

Geographical distribution: Occurs widely across the tropical and subtropical regions of South America. It is extensively recorded throughout Brazil, where it occupies the Amazon basin, the Cerrado, and the vast wetlands of the Pantanal. Its distribution extends westward into Bolivia, southwards through the river systems of Paraguay, and into northeastern Argentina, particularly along the Paraná and Paraguay river basins in provinces such as Formosa, Chaco, and Corrientes, showing a strong association with major South American watersheds.

Habitat: Inhabits a variety of lowland freshwater ecosystems, demonstrating a strong preference for lentic and slow-moving lotic environments. It is commonly found in swamps, marshes, temporary ponds, flooded savannas, and the margins of slow-flowing rivers. The species relies heavily on areas with abundant aquatic vegetation, such as water hyacinths and floating macrophyte mats, which offer essential foraging sites and shelter. While primarily a freshwater species, it occasionally enters brackish waters in coastal marshes and estuaries.

Feeding: Functions as an efficient, opportunistic aquatic predator with a diet dominated by piscivorous prey. It actively hunts underwater, preying on a wide range of small to medium-sized freshwater fish from families like Characidae and Cichlidae. In addition to fish, it feeds heavily on amphibians, including frogs, toads, and their aquatic larvae or tadpoles. Its highly kinetic skull and recurved teeth are evolutionary adaptations that prevent slippery prey from escaping while being swallowed whole underwater.

Behavior: Exhibits both diurnal and nocturnal activity patterns, heavily influenced by ambient temperatures and seasonal water levels, with a peak in activity during crepuscular hours. It is an agile swimmer that spends most of its life in water, often resting just beneath the surface with only its sensory organs exposed. When threatened, it employs defensive tactics such as dorsoventral body flattening to appear larger and more intimidating, occasionally striking if cornered, and releasing a highly pungent foul-smelling cloacal secretion from its musk glands to deter potential predators.

Reproduction: Employs a viviparous reproductive strategy, a physiological trait highly beneficial for aquatic snakes as it eliminates the risk of egg drowning and the need to find dry nesting sites on land. After a gestation period of several months, females give birth to live young, with litter sizes ranging from 5 to 30 neonates. Parturition typically coincides with the onset of the rainy season, when high water levels maximize the availability of microhabitats and small prey. The young are independent from birth and capable of swimming immediately.

Conservation status: Listed as Least Concern (LC) on the IUCN Red List of Threatened Species due to its wide distribution and stable population trends. However, local populations face localized threats from wetland degradation, agricultural expansion, water pollution from pesticide runoff, and human persecution driven by fear and the mistaken identification of this harmless species as a venomous snake due to its defensive posturing.