The River Tāf rises in the Preseli Hills of North Pembrokeshire, near the village of Crymych. Water drains from high ground above the village, and at one time flowed at ground level across the main Cardigan-Tenby road (A478) before falling to the level of the defunct Whitland-Cardigan Railway station "Crymmych Arms"(GWR) where, on the UK Ordnance Survey map of 1866 it is shown as the Source of the Taf.
At this point the stream fulfils its description "Crymych" (Welsh: crooked stream) by turning through almost a right angle along the floor of the valley. The stream is mentioned - with various spellings - in records since 1468CE and provided both the village and its hostelry with an identity. From thence the Taf, augmented by numerous minor tributaries, sweeps south to join the headwaters of the Eastern Cleddau at Aber Taf. For some part of its journey it forms the boundary of Carmarthenshire and Ceredigion. It flows through the town of Whitland before joining the estuary of the River Towy, on the South Wales coast at Laugharne.