The Tambo River (Spanish: Río Tambo) is a Peruvianriver on the eastern slopes of the Andes. The name only refers to a relatively short section; about 159 km (99 mi) long. It starts at the confluence of the Ene and Perené Rivers at the town of Puerto Prado. From here the Tambo River flows 70 km (43 mi) in an easterly direction and then turns north. When merging with the Urubamba River at the town of Atalaya, it becomes the Ucayali River.