Claim: The 42 mile River Taff is located near Cardiff Bay, in Cefn-coed-y-cymmer, Merthyr Tydfil, Wales.
Evidence: 67 km (42 mi) From its confluence at Cefn-coed-y-cymmer, the river flows south, passing several towns. It rises as two rivers in the Brecon Beacons; the Taf Fechan (Little Taff) and the Taf Fawr (Greater Taff) before becoming one just north of Merthyr Tydfil. Its confluence with the River Severn estuary is in Cardiff. It flows underneath the M4 Motorway, before turning southeastward and flowing past the Cardiff suburbs of Radyr, Whitchurch, Llandaff, Pontcanna, the city centre and Grangetown, before emptying into Cardiff Bay, near to the mouth of the River Ely.