The River Taff is a large river in Wales. It is known as the Afon Tāf in Welsh. It is one of the ten major rivers in the United Kingdom.
It rises as two rivers in the Brecon Beacons - the Taff Fechan (Little Taff) and the Taff Fawr (Big Taff), before joining to form the Taff north of Merthyr Tydfil.
The Taff Fawr rises below Corn-Du, south-west of Pen Y Fan and flows south through Beacons Reservoir, Cantref Reservoir and Llwyn-On Reservoir. Underneath Cefn Viaduct, the Nant Ffrwd emerges into the river from a deep, narrow gorge. To the south of Cefn Coed-Y-Cymer, the Taff Fechan and Taff Fawr merge at the wooded confluence that gives Cefn Coed-Y-Cymer its name.
The Taff continues south through the centre of Merthyr Tydfil, where it is joined by the Nant Morlais (locally known as "The Stinky" due to its reputation for pollution) which emerges at Abermorlais from a culvert in the east bank. Just south of Merthyr weir, the Nant Rhydycar joins.
South of Merthyr, the Taff begins to meander its way between Pentrebach and Abercanaid and through Troedyrhiw, Merthyr Vale and Aberfan towards Quakers Yard. At Quakers Yard the river has cut a sharp incised meander, locally known as "Fiddler's Elbow". It is here that the third of the three Taffs, the Taff Bargoed joins the main river.
At Abercynon, it is joined by the Cynon river, and at Pontypridd it is joined by the Rhondda river. From Pontypridd, it runs roughly south, through Taff's Well and Radyr, before arriving at the city of Cardiff in Llandaff.
In Cardiff, the river runs through Bute Park and next to the Cardiff Arms Park and the former National Stadium, now the Millennium Stadium, and into Cardiff Bay, an artificial lake created by the construction of a barrage across the mouth of the river. It then flows out into the Bristol Channel.
The term "Taffy", used as a nickname to people from Cardiff and by extension to all of Wales, is sometimes thought to originate from the name of the river. It may be seen as slightly derogatory. However, it may also be from the name "Dafydd" (David) which is popular amongst the Welsh.
The River Taff is a popular place for the migration of certain fish, including the salmon, river trout and elver.