Aixola Reservoir, reservoir in Eibar, Spain

Aixola Reservoir is a drinking-water reservoir in the Aixola valley between Elgeta (Gipuzkoa) and Zaldibar (Biscay), formed by a 50-metre-high, 195-metre-long gravity dam with a loose-material dike. The dam, at an elevation of 310.5 metres, holds 2.72 hm³ and is fed by the Aixola, Monte erreka and Txulo streams. A 150-metre drainage tunnel carries four outlet pipes, two supplying Eibar.

Eibar's supply came from the Sagar-erreka spring in Placencia de las Armas, captured in 1928, until the Diputación Foral de Guipúzcoa built this dam. Work began on 14 June 1978, designed by Francisco Urquía and built by Agroman under engineers Elósegui and Carmelo del Moral, and ended on 31 December 1981. Filling the reservoir removed six farmsteads, including Beko errota, Balzola-barrena and Aixola-bekua.

The reservoir is named Aixola after the stream it dams, though locals also call it Ariola. Its water, together with the Urkulu reservoir, supplies the Upper Deba network, and two of the outlet pipes in the 150-metre discharge tunnel are reserved for Eibar's drinking water. The shoreline path passes the Lapurdi Gabekoa farmhouse and the ruins of the Bekoerrota mill at the head of the reservoir.

The track bordering the reservoir runs about 4 km around a 2.72 hm³ sheet of water with a 4 km perimeter. Its first stretch is concrete and the rest is dirt, so the surface changes underfoot. Access by road starts in Ermua, at the San Lorenzo district, toward the Zaldibitarra area of Eitzaga; from Elgueta a path signed Aixola Bidea descends past Mount Egoarbitza.

The reservoir drowned six farmsteads, including Bekoerrota, Balzola-barrena, Urbidekurutz, Aixola-bekua and Electra Argiberria, plus the Olazar mill. Locals recall that the same stretch of valley once held up to ten mills, a tile works, two power stations and even a foundry. The ruins of the Bekoerrota mill remain visible at the head of the reservoir.