The
Oiartzun River is a short river in the
Basque Country in the north of the
Iberian Peninsula. It is the smallest river of
Gipuzkoa flowing into the
Bay of Biscay (
Atlantic basin); the river joins the sea at the Bay of
Pasaia. The Oiartzun rises in the
Aiako Harria massif at an altitude higher than 700 m. It flows down through steep slopes and falls, with an average drop to its mouth of 5.49% (600 m drop in the first 5 km).