The Afon Cothi in Carmarthenshire is the largest tributary of the River Tywi in south Wales. From its source at Blaen Cothi in the north of the county, north of Pumsaint, it flows south-east and then turns south-west to flow past Cwrt-y-cadno, Pumsaint, Abergorlech and Pont-ar-Gothi before joining the River Tywi west of the village of Llanarthney.