It is 13 km long, passes through a number of small settlements on the border between Pembrokeshire and Carmarthenshire, and is significant in Welsh legend.

It receives numerous small tributaries: the Sylgen, Barddi, Mamog, Dwrog and Lŵyd on the east side, and the Pedran, Cneifa and Dulas on the west side.

It formed the ancient boundary between the commotes of Emlyn Is Cuch and Emlyn Uwch Cuch,[1] and it today forms part of the boundary between Pembrokeshire and Carmarthenshire.

[2] The river runs through the small settlements of Cwmorgan and Cwmcych, and the village of Abercych.

[5] The valley (Glyn Cuch) is well known in Welsh literature as the place where, in the Mabinogi, Pwyll Pendefig Dyfed has his fateful meeting with Arawn, Lord of the Underworld.