The Manu is a river in southeastern Peru. The Manu River runs down the eastern slopes of the Andes Mountains into the Amazon Basin. It runs through the Manu National Park, a vast Biosphere Reserve, home to arguably the highest concentration of biodiversity on Earth. Few live along its length. Much of the park is off-limits to all but permitted scientists and the indigenous groups of Amazonian Indians , mostly of the Machiguenga tribe. The Manu is a tributary to the Madre de Dios River.