Reports of giant anacondas date back as far as the European colonization of South America, when sightings of anacondas upwards of 50 meters (164 feet) began to circulate amongst colonists, and the topic has been a subject of debate ever since among cryptozoologists and zoologists. Anacondas are well-verified to grow to sizes of 5.21 metres (17.1 ft), and 97.5 kilograms (215 lb). In particular, the green or common anaconda is the heaviest and largest among all extant snakes in terms of robustness, and it is also the second-longest. The longest reputably-measured and confirmed anacondas are about 5.21 metres (17.1 feet) long. Lengths of 50–60 feet have been reported for this species, but such extremes lack verification. Some seemingly reliable claims that can be found describe measured anacondas ranging from 26 to 39 feet, although these remain unverified.
The first recorded sightings of giant anacondas were from the time of the discovery of South America, when early European explorers entered the dense jungles and claimed to have seen giant snakes measuring up to 18 metres (59.1 ft) long. Natives also reported seeing anacondas upwards of 10.5 metres (34.4 ft) to 18 metres (59.1 ft). Anacondas above 5 metres (16.4 ft) in length are rare. The Wildlife Conservation Society has, since the early 20th century, offered a large cash reward for live delivery of any snake of 9 metres (29.5 ft) or more in length, but the prize has never been claimed, despite the numerous sightings of giant anacondas. In a survey of 780 wild anacondas in Venezuela, the largest captured was 5 metres (16.4 ft) long. A specimen measured in 1944 exceeded this size when a petroleum expedition in Colombia claimed to have measured an anaconda which was 11.4 metres (37.4 ft) in length, but its claim has never been proven.
Scientist Vincent Roth claimed to have shot and killed a 10.3 metres (33.8 ft) specimen, but like most other claims, it lacks sound evidence. Another claim of a large anaconda was made by British adventurer Percy Fawcett. Following his 1906 survey of the Bolivia/Brazil border, Fawcett wrote that he had shot an anaconda that measured some 19 metres (62.3 ft) from nose to tail. Once published, Fawcett’s account was ridiculed. Decades later, Belgian cryptozoologist Bernard Heuvelmans came to Fawcett's defence, arguing that Fawcett's writing was generally honest and reliable. Historian Mike Dash writes of claims of even larger anacondas, alleged to be as long as 45 metres (147.6 ft), with some of the sightings supported with photos (although the photos lack scale). Dash noted if reports of a 18 metres (59.1 ft) anaconda strains credulity, then a 120 feet (36.6 m) long specimen would be an impossibility.
The Anaconda has been featured in many stories well known around Latin America, written by famous Uruguayan writer Horacio Quiroga, which even founded the Anaconda Association (a group of Argentine and Uruguayan intellectuals) circa 1920. He also published a book named Anaconda around 1921.
Perhaps the most well-known film portrayal of a giant anaconda in popular fiction is the 1997 film Anaconda, which featured a giant anaconda hunting and killing several crew members from National Geographic, and its sequel Anacondas: The Hunt for the Blood Orchid. Another two sequels and a crossover film, Anaconda 3: Offspring, Anacondas: Trail of Blood and Lake Placid vs. Anaconda were produced as made-for-television films in 2008, 2009 and 2015.
It was featured in an episode of Lost Tapes called "Megaconda".
On the episode "Amazon Assassins" of River Monsters, Jeremy Wade was trying to find and catch a large Arapaima when locals told him about the "Cobra Grande", a giant snake different from the anaconda. The witnesses took him to the spot where they first found the snake, apparently basking. The witnesses claim to have shot the snake three times and that they later found three lumps of lead on the spot where the snake was basking. The witnesses showed Wade a large burrow which they claim the snake escaped into after they shot at it. While he did not find the snake itself, the entrance to the burrow was littered with shed snakeskin.
- Rivas, Jesús Antonio (2000). The life history of the green anaconda (Eunectes murinus), with emphasis on its reproductive Biology (PDF) (Ph.D. thesis). University of Tennessee. pp. 74–80, 111. Retrieved 2016-02-04.
- Soomro, A. 2001. "Eunectes murinus" (On-line), Animal Diversity Web. Accessed January 10, 2008 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eunectes_murinus.html
- Weldon, Kevin (1993). Encyclopedia of Animals: Mammals, Birds, Reptiles, Amphibians. Sydney, Australia: Reader's Digest Association Inc. p. 489. ISBN 1875137491.
- Murphy JC, Henderson RW. 1997. Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons. Krieger Pub. Cous. ISBN 0-89464-995-7.
- Extreme Science: Which is the Biggest Snake?. Accessed January 10, 2008.
- .The Search for the $50,000 Snake. Archived 2009-10-31.
- Krystek, Lee. The Unmuseum: Big Snakes. Accessed January 10, 2008.
- Justice, Aaron. Cryptozoology: Sucuriju Gigante Accessed January 10, 2008.
- Section Bernard Heuvelmans. Accessed January 10, 2008.
- Dash, Mike Borderlands: The Ultimate Exploration of the Unknown; Overlook Press, 2000, ISBN 0-87951-724-7.
- What's stirring in the jungle?. Accessed July 17, 2011.