The Ostola source is on the southern slopes of Monte Capoposto (750 m), in the eastern and hilly part of the
Alpi Biellesi, from which it flows through the
communes of
Soprana,
Mezzana Mortigliengo and
Casapinta. In the territory of
Masserano it receives the waters of Torrente Cigliaga and is blocked by a
dam forming the
artificial lake "delle Piane". Flowing southwards the Ostola receives from the left side its mayor tributary, the Bisingana. It then enters the
Po plain and near
Castelletto Cervo it flows into the
river Cervo. ==References==