Giant anacondas live along tropical waters east of the Andes Mountains and on the Caribbean island of Trinidad. The giant anaconda is the largest snake in the world. Although anacondas and pythons both have been reliably measured at over 9 metres (30 feet) long, anacondas have been reported to measure over 10 metres (33 feet) and are much more heavily built. Most individuals, however, do not usually exceed 5 metres (16 feet).

Giant anacondas lie in the water (generally at night) to ambush caimans and mammals such as capybara, deer, tapirs, and peccaries (peccary) that come to drink. An anaconda seizes a large animal by the neck and almost instantly throws its coils around it, killing it by constriction. Anacondas kill smaller prey, such as small turtles and diving birds, with the mouth and sharp backward-pointing teeth alone. Kills made onshore are often dragged into the water, perhaps to avoid attracting jaguars and to ward off biting ants attracted to the carcass. In the wild, giant anacondas are not particularly aggressive. In Venezuela, they are captured easily during the day by herpetologists who, in small groups, merely walk up to the snakes and carry them off.

Giant anacondas mate in or very near the water. After nine months, a female gives live birth to 14–82 babies, each more than 62 cm (24 inches) in length. The young grow rapidly, attaining almost 3 metres (10 feet) by age three.

Anacondas are members of the boa family (Boidae).