The Anavilhanas Archipelago consists of elongated islands, many thickly forested, formed by the accumulation of sands from the Guyana Hills brought down by the Rio Branco and deposited here in the dark acidic waters of the Rio Negro in a spectacular delta-like formation - the largest inland archipelago in the world.
The Anavilhanas Archipelago has had a protected status since 1997 and is on UNESCO's 'tentative list' as an important ecological site. Manatees are a special feature of this area, and are the emblem species for the site.
Many of the islands are covered by seasonally flooded igapó forest, while slightly higher (and drier) areas support lowland rainforest and sub-montane rainforest - rich environments for plants and wildlife.