[6] In 1830, Johann Georg Wagler erected the separate genus Eunectes for Linnaeus's Boa murina after more and larger specimens were known and described.

Linnaeus almost certainly chose the scientific name Boa murina based on the original Latin description given by Albertus Seba[8] in 1735: "Serpens testudinea americana, murium insidiator" [tortoise-patterned (spotted) American snake, a predator that lies in wait for mice (and rats)].

Linnaeus[5] described the appearance of the Boa murina in Latin as rufus maculis supra rotundatis [reddish-brown with rounded spots on upper parts] and made no reference to a gray coloration.

[18] Reports of anacondas 11–12 m (35–40 ft) or even longer also exist, but such claims must be regarded with caution, as no specimens of such lengths have ever been deposited in a museum and hard evidence is lacking.

[19] The longest and heaviest verified specimen encountered by Dr. Jesús Antonio Rivas, who had examined more than 1,000 anacondas,[20] was a female 5.21 m (17 ft 1 in) long and weighing 97.5 kg (214 lb 15 oz).

[11] In 1937, a specimen shot in Guyana was claimed to have measured 5.9 m (19 ft 4 in) long and weighed 163 kg (359 lb 6 oz).

[21]The color pattern consists of an olive green background overlaid with black blotches along the length of the body.

[19] Reports without physical proof are considered dubious if from non-scientists, as such individuals may at worst be more interested in promoting themselves or telling a good tale, or at the least may not be sufficiently trained in proper measurement methods.

[19] According to the Guinness Book of World Records, this species has been perhaps subject to the most extreme size exaggerations of any living animal.

To prove the point of overestimating, in Guyana in 1937, zoologist Alpheus Hyatt Verrill asked the expedition team he was with to estimate the length of a large, curled-up anaconda on a rock.

[23] While in Colombia in 1978, herpetologist William W. Lamar had an encounter with a large female specimen 7.5 m (24 ft 7 in) long, estimated to weigh between 136 and 180 kg (300 and 397 lb).

[23] A specimen of 7.3 m (23 ft 11 in), reportedly with a weight of 149 kg (328 lb), was caught at the mouth of the Kassikaityu River in Guyana, having been restrained by 13 local men, and was later air-lifted for a zoo collection in the United States, but died in ill health shortly thereafter.

[23] The largest size verified for E. murinus in captivity was for a specimen kept in Pittsburgh Zoo and PPG Aquarium, which grew to a length of 6.27 m (20 ft 7 in) by the time she died on July 20, 1960.

[32] The range of these specimens, some of which were able to evade capture, spans from Gainesville to Homestead, Florida - a distance of over 350 miles (560 km).

However, the ecological, economic, and safety risks posed by their existence in the state are deemed 'very high' by the Florida Fish and Wildlife Conservation Commission, with the ecological threat reaching the extreme risk level, as introduced anacondas are apex predators, able to compete with Florida's native species.

[33] Anacondas live in swamps, marshes, lagoons, and slow-moving streams and rivers, mainly in the tropical rainforests and seasonally flooded savannas of the Amazon and Orinoco basins.

Their eyes and nasal openings are on top of their heads, allowing them to lie in wait for prey while remaining nearly completely submerged.

Their eyes and nose are located on the top of the head, allowing the snake to breathe and watch for prey while the rest of the body is hidden underwater.

[37] Anacondas are apex predators with a wide variety of prey, almost anything they can overpower, including fish, amphibians, birds, various mammals and other reptiles.

Scientists hypothesize several explanations, including the great sexual dimorphism of the species, and a female's need for food after breeding to sustain the long gestation.

[42] Although this species is an apex predator, even adult specimens are part of the diet of jaguars, black caimans and Orinoco crocodiles.

Mating approaches its climax when the stimulus of the males' spurs induces the female to raise her cloacal region, allowing the cloacae of the two snakes to move together.

[35] In 2014, green anaconda in West Midland Safari Park gave birth to three young through parthenogenesis.

The 2023 Guinness Book of World Records for the oldest living snake in captivity is a green anaconda aged 37 years 317 days, verified on 14 May 2021 by Paul Swires, at Montecasino Bird & Reptile Park in Johannesburg, South Africa.

[49] Anacondas have been portrayed in horror literature and films, often incredibly gigantic, agile and with the ability to swallow adult humans.

Despite having the capability to overpower a man, there is no verified evidence of this species consuming humans, unlike the reticulated python.

This is possibly because large specimens inhabit remote areas deep inside the Amazon jungle, which is isolated from humans, unlike the python in Asia.