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 may represent an Old Gaelic adaption of Brittonic *wergÃÂ, meaning "anger" (cf. Welsh gwery).
The river was once a boundary of the Lordship and Barony of Balvaird.
The river was polluted with aluminium sulphate killing nearly all of the fish in May 2014. Scottish Water was fined ã8,000 for the incident.