The Reserva Faunística Cuyabeno, one of Ecuador’s largest reserves, encompasses over six thousand square kilometres of rainforest, holding the Río Cuyabeno basin and much of the watershed of the lower Río Aguarico as far as the Peruvian border. Protecting areas with species that survived the last ice age, Cuyabeno harbours abundant birdlife with 494 recorded species (a number that continues to grow) and a staggering 228 tree species per hectare. The reserve also contains a huge network of lakes and lagoons, including fourteen major interconnected bodies of water and large areas of inundated forest. Among them are two main black-water lake systems: the Cuyabeno Lakes, which include the Laguna Cuyabeno and Laguna Grande, and Lagartococha, at the eastern end of the reserve bordering Peru. In contrast to the nutrient-rich whitewater rivers originating in the Andes, black-water rivers typically form where there is little soil sediment and generally originate in the Amazon basin itself; the water takes on a dark tea-like colour from the vegetable humus that falls into it, which also makes it very acidic and rich in tannins. Some people come to the reserve specifically to see its aquatic wildlife, such as pink freshwater dolphins, turtles, black caiman, anaconda, manatee, giant otters, countless colourful frogs and toads and 450 species of fish.
The boundaries of the reserve have changed since its creation in 1979, particularly following major incursions by oil companies and settlers into the western areas around Tarapoa. The governments of the time largely ignored this destruction, but in 1991, after considerable pressure from international agencies and CONAIE (Confederation of Indigenous Nationalities of Ecuador), a vast tract of land on the eastern side was added, almost tripling the size of the reserve. While the reserve is now less accessible to colonizers and far better protected by politically active indigenous communities (including Kichwa, Cofán, Secoya, Siona and Shuar), who are struggling to defend their cultures and territory against oil company encroachment, oil extraction is still causing problems through toxic waste and spills that have drained into the Cuyabeno basin.