The River Sirhowy (Welsh: Afon Sirhywi) is a river in south Wales and a tributary of the River Ebbw.
The River Sirhowy has its source on the slopes of Cefn Pyllau-duon above Tredegar. After flowing through Si�n-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.
Extensive mining in the Sirhowy valley, for metals as well as for coal, has led to considerable pollution of the river in the past, though water quality is now improving.