Pacaás Novos River  The Pacaás Novos River () is a river of Rondônia state in western Brazil. It is a tributary of the Mamoré River, which it joins from the right just above Guajará-Mirim. The Pacaás Novos River rises in the mountains in the west of the Pacaás Novos National Park and flows west from there through the Rio Pacaás Novos Extractive Reserve. The Ouro Preto River, a right tributary that flows from the east through the Rio Ouro Preto Extractive Reserve, joins the Pacaás Novos River on the west boundary of the reserve, which is defined by this section of the Pacaás Novos.