Then past Bedwas, Trethomas, Machen, Draethen, Llanrumney and Rumney and its estuary into the River Severn.
Sourced within the valley, on the southern edge of the Brecon Beacons, the Rhymney River descends steeply through the town of New Tredegar towards Ystrad Mynach, and then onwards south across a flat plain before entering the Severn Estuary to the east of Cardiff.
Covering a distance of 30 miles (48 km), the catchment is divided into two distinct parts:[2] Being located in part of the South Wales coalfield and South Wales Valleys iron-producing area, the resultant black river had poor water quality through most of the 19th and 20th centuries.
The river is culverted in many of its upper sections, including a tunnel under the former factory complexes in Rhymney, exiting at Pontlottyn.
[3] Since the closure of the last of the coal mines in the late 1980s, the water has become much cleaner and is now full of fish and insect life and supports plenty of other wildlife.