The River Clarin () is a fast-flowing river in Ireland, flowing through southern County Galway.
The River Clarin rises in the townland of Gortnalone, north of Attymon and snakes westwards, turning southwards through Athenry. Athenry Castle was built at a fording point on the river. It flows southwestwards and passes under the N18 at Clarinbridge and enters Dunbulcaun Bay.
Fish species include Crayfish, trout, salmon, lamprey and eel.