The Teles Pires is a 1,370 km long river in Brazil. The river flows through the state of Mato Grosso and its lower part marks the border between the states of Mato Grosso and Pará. At its mouth it joins Juruena River and together they form the Tapajós, which is one of the biggest tributaries of the Amazon River. The most important settlement along the river is A…The Teles Pires is a 1,370 km long river in Brazil. The river flows through the state of Mato Grosso and its lower part marks the border between the states of Mato Grosso and Pará. At its mouth it joins Juruena River and together they form the Tapajós, which is one of the biggest tributaries of the Amazon River. The most important settlement along the river is Alta Floresta. One writer says that it was originally called the Paranatinga, and was renamed after Captain Telles Pires who died exploring the river in 1889.