Of the Rhondda’s two major tributaries, the Rhondda Fawr rises near Llyn Fawr and runs down the Rhondda Valley, through Treorchy, Tonypandy and Porth, to its confluence with the River Taff at Pontypridd. The Rhonnda Fach has its source near to the Rhondda Fawr on the hills above Blaenrhondda and it joins its sister tributary at Porth.
Improving water quality since the early 1970’s has followed the closure of all the Rhondda’s coal mines, while investment in improving sewerage and sewage treatment have also had major benefits. There are several fishing clubs, one of which has its own trout farm. Salmon are now running in the river again, and there is some evidence of spawning.