What is "ibaizabal"

The Ibaizabal river (wide river in Basque) drains southeastern Biscay to the Estuary of Bilbao. It is long from its source at Elorrio to the Nervion, and it passes by the towns of Durango and Amorebieta and joins the Nervion river at Basauri. Both rivers run then together for a short length until they merge with the sea at Bilbao. It is disputed which river is the one that actually reaches Bilbao. It is commonly agreed that it is the Nervion, but there are some who argue that the Ibaizabal carries more water (see name controversy).