One of these, the Valira del Norte (24 km), and its principal tributary, the Arinsal River, drain western Andorra.
The Valira del Orien (28 km) drains the eastern part and has a tributary, the Madriu.
The two branches unite in southwest Andorra to form the Gran Valira which leaves the country to join the Segre River 11 km south of the border in northeastern Spain.