Onyar

250px|thumb|"Cases del Onyar", next to the Onyar River in Girona

The Onyar (; Spanish: Oñar ; Undarius in Latin) is a Spanish river in Girona, Catalonia that begins at the Guilleries massif at the apex of the Catalan Transversal Range and the Pre-Coastal Range. It joins the Ter at the city of Girona, and crosses the city from south to north, separating the city into the old part (on the right side) and the more modern part (on the left side).