Absolutely correct. It starts at the Taff just above Blackweir, it and the Taff almost make Blackweir an island. It feeds the castle moat then the docks. There is another stream that runs right down from above Thornhill Cemetry right through Whitchurch along Merthyr Road and down the middle of Cathedral View in Gabalfa to the river. It used to be open but is now mostly covered, but it's still there.