The archetypal Welsh coal valley river — two branches, Rhondda Fawr and Fach, meeting at Porth before joining the Taff at Pontypridd. Coal extraction peaked here at 9.5 million tonnes a year in 1913; the last colliery (Maerdy) closed in 1990. NRW's own Water Framework Directive data tracks the recovery precisely: the Fawr has gone Poor-Poor-Good across three assessment cycles, the Fach Poor-Poor-Moderate — a genuine, still-improving 'phoenix river' story, not a finished one. Grayling are present but geographically limited to the lower river near the Taff confluence; further up the valley it's wild brown trout only.
- Carboniferous coal measures

