The green anaconda is the heaviest snake on Earth and one of the most powerful aquatic predators of tropical South America, a semiaquatic constrictor whose presence reflects the health of the wetlands, flooded savannas, and river systems it depends on [IUCN 2021]. Long the subject of myth and exaggeration, the species has been studied rigorously only in recent decades, most notably through a multi-decade field program in the Venezuelan Llanos that captured and measured hundreds of wild individuals [Rivas 2000]. This profile examines the snake's biology, the pressures it faces across its enormous range, and the work underway to keep its habitats intact.
Biology and Identification
The green anaconda is a heavy-bodied boid with olive-green dorsal coloration overlaid by paired dark blotches, and a distinctive orange-yellow striped pattern on each side of the head [USGS NAS 2024]. It is among the longest snakes in the world and the most massive: large wild females commonly exceed 5 m in total length, while males are markedly smaller [Rivas et al. 2007]. The species displays one of the most extreme degrees of female-biased sexual size dimorphism documented in any terrestrial vertebrate, with adult females substantially longer and heavier than males [Rivas et al. 2007].
As an ambush predator strongly tied to water, the green anaconda preys on a broad range of vertebrates, including fish, birds, caimans, and large mammals such as capybaras; prey is killed by constriction and swallowed whole [USGS NAS 2024]. The species is ovoviviparous, with females retaining developing embryos internally and giving birth to live young after a gestation of several months [Rivas 2000]. Reproduction in studied populations is concentrated in the dry season and is characterized by multi-male breeding aggregations, in which numerous males compete to mate with a single much larger female [Rivas et al. 2007].
A 2024 genetic study reorganized the long-standing concept of the species, identifying two deeply divergent lineages within what had been treated as a single green anaconda and describing the northern populations as a separate form [Rivas et al. 2024]. The validity and naming of that northern lineage are actively contested on nomenclatural grounds in the peer-reviewed literature [Dubois et al. 2024], and Eunectes murinus in its traditional, widely recognized sense remains the binomial under which the species is assessed by conservation authorities.
Habitat and Range
The green anaconda occupies tropical South America east of the Andes, spanning the Orinoco and Amazon basins and associated drainages across countries including Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia, and Brazil [USGS NAS 2024]. It is closely associated with slow-moving and still water: oxbow lakes, streams, rivers, palm swamps, and the seasonally flooded grasslands of the Llanos [Avery et al. 2025].
Radio-telemetry and survey work in the western Amazon found individuals using well-vegetated embankments and log jams as basking sites, and otherwise remaining concealed beneath fallen logs, submerged vegetation, undercut banks, and detritus — behavior that makes the species cryptic and difficult to census despite its size [Avery et al. 2025]. Seasonal flooding strongly shapes movement and habitat use, with home ranges contracting sharply as waters recede in the dry season [Rivas 2000].
In accordance with NRWL sensitive-species policy, specific basking-site locations, aggregation coordinates, and seasonal movement details are not disclosed in this article.
Conservation Status
The green anaconda is listed as Least Concern on the IUCN Red List, assessed in 2021, on the basis of its very wide distribution, presence across numerous protected areas, and the absence of evidence for a range-wide population decline sufficient to warrant a threatened category [IUCN 2021]. The assessment notes that the species is not considered to be declining at a rate approaching the thresholds for listing, while acknowledging localized pressures.
The species is included on CITES Appendix II, which regulates international commercial trade in live animals and skins to ensure it does not threaten wild populations [CITES 2023]. A Least Concern listing reflects the global picture and does not imply the species is secure everywhere: subpopulations in heavily converted or oil-developed landscapes face habitat loss and direct killing that are not captured by a range-wide category [USGS NAS 2024].
Threats
Habitat loss and degradation are the most significant pressures on the green anaconda. Drainage of wetlands for agriculture and ranching, deforestation, and the development of oil infrastructure in parts of Colombia, Peru, and Venezuela reduce and fragment the aquatic and floodplain habitats on which the species depends [USGS NAS 2024].
Direct killing occurs across the range. Green anacondas are killed out of fear by people who encounter them near water and human settlements, and they are hunted for their skins for the leather trade and, in some regions, for fat used in folk medicine [USGS NAS 2024].
Collection for trade adds further pressure: live animals enter the international and domestic pet trade, and raw skins are exported to tanneries — the activities that place the species under CITES Appendix II monitoring [CITES 2023].
Pollution and water-quality change in major basins, together with the disturbance of floodplain hydrology, can degrade prey availability and the still-water habitats the species favors [USGS NAS 2024].
What Is Being Done
International trade controls. CITES Appendix II listing requires that exports of green anaconda specimens be accompanied by permits and a finding that trade is not detrimental to wild populations, providing a framework for monitoring and limiting commercial offtake [CITES 2023].
Long-term field research. Sustained scientific study — beginning with a multi-decade mark-and-recapture program in the Venezuelan Llanos that measured hundreds of wild snakes — has replaced anecdote with quantitative data on growth, reproduction, diet, and movement, giving managers a factual basis for conservation [Rivas 2000; Rivas et al. 2007].
Taxonomic clarification. The 2024 genetic reassessment of the genus, and the published scientific debate that followed, are sharpening understanding of how many distinct lineages exist and where each occurs — information that directly affects how conservation status and management should be partitioned across the range [Rivas et al. 2024; Dubois et al. 2024].
Habitat and survey work. Collaborative habitat-use studies in the western Amazon are improving the ability to detect and monitor this cryptic species, informing protected-area planning in regions such as the Madre de Dios basin of Peru [Avery et al. 2025].
Invasive-species surveillance. Outside its native range, agencies track records of escaped or released individuals — for example through the U.S. Geological Survey's nonindigenous aquatic species program — to prevent establishment in vulnerable wetland systems [USGS NAS 2024].
How Readers Can Help
Citizen science. Photograph and log wildlife observations through platforms such as iNaturalist. Verified occurrence records contribute to range mapping and to monitoring for the species both within and beyond its native distribution.
Informed consumer choices. Avoid purchasing exotic-leather goods or wild-caught reptiles. Demand for skins and the pet trade are documented pressures on the species, and CITES Appendix II controls work only when buyers reject illegally sourced products [CITES 2023].
Support wetland protection. Back organizations and policies that conserve tropical floodplains, palm swamps, and river systems. Because the green anaconda is an indicator of intact aquatic habitat, protecting these systems benefits entire wetland communities [Avery et al. 2025].
Education outreach. Share accurate, science-based information about anacondas to counter the fear-driven killing that follows exaggerated accounts of the species. Documented persecution near human settlements is a measurable local threat [USGS NAS 2024].
References
[Avery et al. 2025] Avery, T., Swing, K. & Leite Pitman, R. (2025). Habitat use of cryptic Green Anaconda (Eunectes murinus) in the western Amazon. Journal of Natural History, 59(17–20), 1141–1165. https://doi.org/10.1080/00222933.2025.2479875
[CITES 2023] CITES. (2023). Appendices I, II and III. Convention on International Trade in Endangered Species of Wild Fauna and Flora. Eunectes murinus is listed in Appendix II. https://cites.org/eng/app/appendices.php
[Dubois et al. 2024] Dubois, A., Bauer, A.M., Ceríaco, L.M.P., Ohler, A. & 9 others. (2024). Nomenclatural problems raised by the recent description of a new anaconda species (Squamata, Serpentes, Boidae), with a nomenclatural review of the genus Eunectes. Bionomina, 37(1), 8–58. https://doi.org/10.11646/bionomina.37.1.1
[IUCN 2021] IUCN. (2021). Eunectes murinus (Green Anaconda). The IUCN Red List of Threatened Species 2021: e.T44580041A44580052. Category: Least Concern (assessed 2021). https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T44580041A44580052.en
[Rivas 2000] Rivas, J.A. (2000). The life history of the green anaconda (Eunectes murinus), with emphasis on its reproductive biology. Ph.D. dissertation, University of Tennessee, Knoxville. https://trace.tennessee.edu/utk_graddiss/8391/
[Rivas et al. 2007] Rivas, J.A., Muñoz, M.C., Burghardt, G.M. & Thorbjarnarson, J.B. (2007). Sexual size dimorphism and the mating system of the green anaconda (Eunectes murinus). In: Henderson, R.W. & Powell, R. (eds.), Biology of the Boas and Pythons, pp. 313–325. Eagle Mountain Press, Eagle Mountain, Utah. https://www.nmhu.edu/our-faculty/jesus-rivas/
[Rivas et al. 2024] Rivas, J.A., De La Quintana, P., Mancuso, M., Pacheco, L.F., Rivas, G.A., Mariotto, S., Salazar-Valenzuela, D., Tepeña Baihua, M., Baihua, P., Burghardt, G.M., Vonk, F.J., Hernandez, E., García-Pérez, J.E., Fry, B.G. & Corey-Rivas, S. (2024). Disentangling the anacondas: revealing a new green species and rethinking yellows. Diversity, 16(2), 127. https://doi.org/10.3390/d16020127
[USGS NAS 2024] U.S. Geological Survey. Nonindigenous Aquatic Species Database. Eunectes murinus (Green Anaconda) — Species Profile. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=2636