| Afon Twrch | |
|---|---|
 Afon Twrch looking south downstream from the side of Pen yr Helyg | |
| Etymology | afon / 'river' and twrch / 'boar'. |
| Location | |
| Country | Wales |
| Physical characteristics | |
| Source | |
| • location | Southern slopes of Bannau Sir Gaer (Carmarthen Fans) and Fan Brycheiniog |
| • coordinates | 51°52′49″N 3°42′39″W / 51.880359°N 3.710933°W |
| • elevation | 770 metres (2,530 ft) |
| Mouth | |
• location | River Tawe at Ystalyfera |
• coordinates | 51°45′40″N 3°46′55″W / 51.761194°N 3.782022°W |
• elevation | 70 metres (230 ft) |
| Length | 8.7 miles (14 km) |
| Basin features | |
| River system | River Tawe |
| Tributaries | |
| • left | Nant Gwys |
| • right | Nant Lluestau, Nant Manyn, Nant Y Ddraenen, Twrch Fechan, Nant Y Llyn, Nant Llynfell |
The Afon Twrch is a river which rises in the Black Mountain in south Wales. It forms the boundary between the counties of Brecknockshire (currently administered as part of the unitary authority of Powys) and Carmarthenshire and, downstream of Ystradowen, between Brecknockshire and Glamorgan (and unitary authorities of Powys and Neath Port Talbot).