Nervion

Nervión is a river that runs through the town of Bilbao, Spain into the Cantabrian Sea (Bay of Biscay). Its lowermost course, downstream of its confluence with the Ibaizabal River, is known as the Estuary of Bilbao.

The river is 72 kilometres (45 mi) long from its source at the Burgos and Alava provincial limits to the sea and runs in a South to North direction.

Soon after its source, the river forms a spectacular 300-metre (980 ft) waterfall in the Delika canyon (Alava) and then enters the Biscay province through the city of Orduña. This waterfall is the largest in Spain with its 222 metres. It re-enters Alava through the towns of Amurrio and Llodio.

The river then runs back into Biscay province and out to the Cantabrian sea, entering the Bilbao metropolitan area at Ugao-Miraballes. The tidal influence reaches 15 kilometres (9 mi) inland from the sea, in Bilbao.

The main tributaries are:

From the west: Cadagua and Galindo.
From the east: Arratia, Ibaizabal and Asua.

The Ibaizabal is considered by some to be an equally important river, so the whole system is often called Nervión-Ibaizabal and the final tract just Estuary of Bilbao. The basin area is 1,900 square kilometres (730 sq mi).