The Oca river is a short river, about 70 kilometres 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 metres long and 100 metres high, was of great strategic value in the 11th century and was defended by the castle of Alba.
