The River Farg is a small tributary of the River Earn, located in the lieutenancy area of Perth and Kinross, central Scotland. Its source is located in Glen Farg reservoir; it winds round roads and farms, and has been forced in many places to change course due to human interference. It ends in a confluence where it joins the Earn.

The name Farg means "wrathful" in Manx, referring to the force of the river when in spate.