Afon Gwydderig

The River Gwydderig or Afon Gwydderig in Welsh is a tributary of the River Bran (Welsh: Afon Bran). It's headwater is found in Bwlch-y-groes Mountain, about 3 miles (4.8 kilometres) North of the small village of Llywel, Powys. The A40 runs next to the river from Llywel as far as Llandovery, Carmarthenshire.

The Gwydderig crosses the boundary between Powys and Carmarthenshire at the village of Halfway. It joins the Bran in Llandovery, Carmarthenshire, about 1.5 miles upstream of the confluence of the Bran with the River Towy. The River Gwydderig therefore forms part of the Towy's catchment basin and drains into the Bristol Channel at the Towy estuary.