Rivers

Most of the rivers in the area have their sources in the Gibijo hills, on the slopes of Gorbeia, in the hills of Arangio/Urkiola or in the hills of Legutiano/ Elgea. These hills and the Urkilla and Altzaina hills run from west to east and form the watershed between the Bay of Biscay and the Mediterranean.

Around 20% of the overall surface area of the district belongs to the Bay of Biscay basin. The rivers in this part of the district are usually short and fast-flowing, and carry a great deal of water. Two sub-basins can be distinguished: that of the river Altube (an affluent of the Nervión), located between the municipalities of Urkabustaiz and Zuia; and that of the Aramaiona (an affluent of the Deba) in the municipality of the same name. The Nervión does not originate in this district, but many of its tributaries run down from the hills of Urkabustaiz, sometimes with drops of over 250 m.

The rivers flowing into the Bay of Biscay cause greater erosion than those flowing into the Mediterranean, and have thus carved out some truly beautiful terrain, especially around the waterfalls of Goiuri and Nervión in Urkabustaiz, and the mountain peaks around the Aramaio.

The rivers in the rest of the district belong to the Mediterranean Basin, and carry less water down less pronounced slopes. Four major sub-basins can be distinguished: that of the Bayas, a direct tributary of the Ebro, which includes the Zuia valley and part of Urkabustaiz; that of the Zubialde, which covers most of Zigoitia; that of the Undebe between Zigoitia and Legutiano; and that of the Urkiola and Olaeta in the municipality of Aramaio.

These last rivers run into the river Zadorra (the longest and biggest in Alava/ Araba); The Zubialde runs into it directly and the Undebe, Urkiola and Olaeta run into the Santa Engracia reservoir at Legutiano. Between Aramaio and Legutiano stands the small Albina reservoir, which is in fact a small river basin opening onto the Urrúnaga reservoir.

The waters of the Zadorra are dammed to form the Ullibarri-Gamboa reservoir in Arrazua-Ubarrundia. This reservoir is fed by small streams running down from the Elgea hills as well as by the Zadorra itself, and the whole of the municipality lies within the Zadorra basin.

The rivers have long served the local people as a source not only of drinking water but also of power to drive flour mills, electric power stations, iron-works, wash-houses, etc., and there are many interesting buildings associated with these uses.

Their main use at present is recreational: the reservoirs are home to sailing schools, recreation areas, fishing reserves, bathing areas, etc. The stretch of the river Bayas between Zuia and Urkabustaiz provides some of the best fishing in the province.