The source of the Farg is to be found in the Glen Farg reservoir. From here 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 appears to be the Gaelic for "wrathful" (a word now found only in Manx Gaelic), referring to the force of the river when in spate.
The river was polluted with aluminium sulphate killing nearly all the fish in 2015. Scottish Water was fined £8,000 for the incident.
- Location map: 56°20’41"N, 3°20’41"W
- 'Scottish Water fined after fish killed by chemical leak': BBC 24 February 2015