[1] Its tributary is the Afon Tafolog, which drains the eastern slopes of Drum, a mountain in the Carneddau range.

The river originates from several small streams on the southern slopes of Tal y Fan, to the east of Bwlch y Ddeufaen.

The highest of these streams originates approximately 480 meters up just south of the western summit of Tal y Fan.

Other streams come from a little to the east and flow close to the old Poet's Stone (Maen y Bard).

It turns east again passing the site of the Roman fort of Canovium to flow into the River Conwy at the end.