The Anavilhanas National Park is a Brazilian conservation unit created to protect the Anavilhanas Archipelago and its biodiversity. Located in the Rio Negro basin, this is the second largest river archipelago in the world, with around 400 islands and lakes, and is home to endangered species such as the Amazon river dolphin (Inia geoffrensis), the tucuxi dolphin (Sotalia fluviatilis) and the Amazonian manatee (Trichechus inunguis). Rio Negro is the largest blackwater river in the world and has this color because its waters are dyed by humic acid, released by the submerged foliage of the trees. Running slowly, the river has high acidity which reduces the proliferation of mosquitoes.