Santa Engracia River, Mountain river in Álava, Spain

The Santa Engracia River originates in the mountains of Álava and flows through protected natural areas. Its path winds through the landscape for several kilometers before joining larger water systems in the region.

The river rises near the Barazar pass in the Gorbea natural park, on the Álava–Biscay border, and for part of its course is called Undebe. It forms the provincial boundary until San Juan in Ubidea, then separates Cigoitia from Villarreal de Álava. The Urrúnaga reservoir, built in 1957, is the main feature of its course; in June 2015 the Zadorra reservoirs were declared a Special Area of Conservation.

The river's name comes from Santa Engracia, and in its upper course it is called Undabe or Undebe. It forms the boundary between Álava and Biscay until it reaches San Juan in Ubidea, then separates the municipalities of Zigoitia and Legutio. Its main tributaries are the Urkiola, Iraurgi, Olaeta and Albiña.

The river rises near the Barazar pass in the Gorbea natural park, at 620 m, and runs 27 km to the Zadorra below the Urrúnaga reservoir, at about 510 m. Upstream it is called Undebe and marks the Álava–Biscay border until San Juan in Ubidea. The reservoir, built in 1957, is the main feature of its course.

The river rises near the Barazar pass in the Gorbea natural park, at 620 m, and for part of its course is called Undebe, forming the boundary between Álava and Biscay until it reaches San Juan in Ubidea. Its main tributary is the Urquiola, and the Urrúnaga reservoir, built in 1957, collects the waters of both.