The Oca river is a short river, about 70 km long, in the north of Spain. It is an affluent of the Ebro river that flows through the province of Burgos. It begins in the Sistema Ibérico range and flows north through the municipalities of Rábanos, Villafranca Montes de Oca, Valle de Oca, Alcocero de Mola, Prádanos de Bureba, Briviesca, Vileña, the shire of Bureba and Oña. The Oca River rises in the comarca of Montes de Oca, near the town of Rábanos. Near its source, the river passes through the narrow, rock-lined gorge of La Hoz. This passage, 700 m long and 100 m high, was of great strategic value in the 11th century and was defended by the castle of Alba.

Affluents

From the right, the Oca receives the waters of the river Matapán and the streams Valsorda and Penches, while on the left it receives the waters of the rivers Cerratón, Anguilas and Homino, and the streams Valdazo and Hoyo.