Rio Oja is a river in the
La Rioja province of northern Spain. It flows through the
Oja Valley past the town and municipality of
Ezcaray. It is generally accepted to have given its name to the famous wine of the Rioja DO, although there are other theories. The Oja flows into the
Tirón River east of
Cihuri, and the Tirón flows into the Ebro immediately north of
Haro.