The river is about sixteen miles long. The source is on Staple Hill, Somerset in the Blackdown Hills, and for here it flows on a roughly southern course through Bishopswood, to form the border between Devon and Somerset, passing through and on to Marsh on the A303 and on southward to a point east of Yarcombe, where Somerset ends. The Yarty runs just west of the meeting point of the three counties, Devon, Somerset and Dorset, below which it resumes border duty for a short while, between Devon and Dorset.
The Yarty continues to form a river valley for much of the rest of its course, passing between Yarcombe, Stockland, Dalwood and Membury until it meets the River Axe just southwest of Axminster, which carries its waters to the English Channel.
The A303 trunk road crosses the Yarty on a high viaduct at Marsh. Further south, the A30 trunk road crosses the river east of Yarcombe, slightly west of the border of Devon with Dorset border.
The upper area forms one of several bisections of the otherwise hilly area around the Blackdown Hills. As the river is based in a relatively deep valley, it is prone to flooding. There have been numerous formally recorded reports of property damage near the Yarty since the 1960s.
The land across the flood plain of the Yarty is boggy and difficult to cross. In the late spring of 1685 during the Monmouth Rebellion, this caused problems when Lord Albermarle's army were unable to defend the advancing force of the Duke of Monmouth northwards from Lyme Regis towards Sedgemoor.
- Location map:50°46’13"N, 3°1’6"W
- "Yarty". Catchment Data Explorer. Environment Agency. 31 March 2016. http://environment.data.gov.uk/catchment-planning/WaterBody/GB108045015130. Retrieved 16 August 2016.
- Mills, David (2011). A Dictionary of British Place-Names. Oxford University Press. ISBN 978-0-199-60908-6.
- "Circular Walk : Otterford and the Yarty Valley". Visit Somerset. http://www.visitsomerset.co.uk/downloads/dmsimgs/Circular%20Walk%20-%20Otterford_516754477.pdf. Retrieved 16 August 2016.
- Flood Investigation Report, December 2012 (Devon County Council) p26
- Scott, Christopher (2016). The Maligned Militia: The West Country Militia of the Monmouth Rebellion, 1685. Routledge. ISBN 978-1-317-02461-3.