The Juruena River (Portuguese: Rio Juruena) is a 1,240 km (770 mi) long river in west-central Brazil, in the state of Mato Grosso. It originates in the Parecis plateau. For the last 190 km (120 mi) of its lower part the river becomes the border between the states Mato Grosso and Amazonas. It finally joins the Teles Pires river to form the Tapajós river, which is one of the biggest tributaries to the Amazon River.