The
Pisuerga is a
river in northern
Spain, the
Duero's second largest
tributary. It rises in the
Cantabrian Mountains in the province of
Palencia, autonomous region of
Castile and León. Its traditional source is called Fuente Cobre, but it has been discovered that the real source is a glacier higher in the mountains. The river flows south into the
Douro river shortly after passing through the city of
Valladolid. Its length is approximately .