The Oria is a river in the Basque Country at the north of the Iberian Peninsula. Its one of a series of Basque rivers flowing into the Bay of Biscay (Atlantic basin) and the main river of the province Gipuzkoa in volume (25.6 m3/s), length (75 km) and basin (882.5 km2), the main feature of these rivers aligned south to north being their shortness. The maximum elevation at the source is 1,260 m, while at its lowest height the tidal influence extends inland up to Usurbil (estuary). On this final stretch, many marsh and wetland strips dotted the banks of the Oria, although some of them have been drained for agricultural and building purposes.
