The River Gwydderig or Afon Gwydderig in Welsh

Welsh language

Welsh is a member of the Brythonic branch of the Celtic languages spoken natively in Wales, by some along the Welsh border in England, and in Y Wladfa...

 is a tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the River Bran

Afon Brân

The Afon Brân is a tributary of the River Towy in mid Wales. Its headwaters rise in Irfon Forest in the northeastern corner of Carmarthenshire as the Cynnant Fawr and Afon Lwynor and the river assumes the name of Afon Brân at their confluence to the north of the village of Cynghordy. Its major...

 (Welsh: Afon Brân). It rises as the Nant Gwydderig on the southern slopes of Mynydd Bwlch-y-groes, about 3 miles (4.8 km) North of the small village of Llywel

Llywel

Llywel is a small village that gives its name to Llywel community in Powys, Wales. The main settlement in the community is Trecastle. According to the 2001 Census the population of Llywel community is 524.- Location :...

, Powys

Powys

Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...

. The A40

A40 road

The A40 is a major trunk road connecting London to Fishguard, Wales and officially called The London to Fishguard Trunk Road in all legal documents and Acts...

 runs next to the river from Llywel as far as Llandovery

Llandovery

Llandovery is a market town in Carmarthenshire, Wales, lying on the River Tywi and the A40 road.The town is served by Llandovery railway station, where there is a park and ride to Llanelli and Shrewsbury via the Heart of Wales Line...

, Carmarthenshire

Carmarthenshire

Carmarthenshire is a unitary authority in the south west of Wales and one of thirteen historic counties. It is the 3rd largest in Wales. Its three largest towns are Llanelli, Carmarthen and Ammanford...

.

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

Bristol Channel

The Bristol Channel is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Severn to the North Atlantic Ocean...

at the Towy estuary.