It rises just south of Hacketstown, County Carlow.

It flows southeast to Tinahely, being accompanied by the R747 regional road for the distance.

It flows under Clonegal Bridge at a point where it divides Clonegal, County Carlow to the west from Watch House Village, County Wexford, to the east.

A few kilometres further downstream it flows into the River Slaney.

Derry Water River is a separate tributary, which rises near Tinahely and flows north-eastwards to form the Aughrim River.