The Sirhowy River has its source on the slopes of Cefn Pyllau-duon above Tredegar. After flowing through SiƓn-Sieffre's Reservoir it turns south through Tredegar and then Blackwood and Pontllanfraith. It turns eastwards near Cwmfelinfach and joins the River Ebbw near Crosskeys.
History
Extensive mining in the Sirhowy valley, for metals as well as for coal, had led to considerable pollution of the river in the past (it was known locally as the "Black River"), though water quality is now improving.