Two branches — Ebbw Fawr and Ebbw Fach, meeting at Aberbeeg — that ran effectively dead through the 1970s: coal washeries and the Ebbw Vale steelworks discharged a cocktail of chemical waste that stopped even eels reaching the lower river, and a resident kingfisher pair had to hunt the adjacent canal instead. Pollution controls from the mid-1970s brought fish back in a documented sequence (trout, then eel, stone loach, stickleback, bullhead), and the lower river is now rated as some of the best wild brown trout fishing in Wales. The honest caveat: a historic mine-water discharge at Six Bells, on the Ebbw Fach, still requires active, ongoing treatment infrastructure — this is a genuine recovery story, not a finished or pristine one.

• Carboniferous coal measures