Rhaeadr Cynfal

The River Dwyryd (Welsh: Afon Dwyryd, meaning a river of two fords) is a river in Gwynedd, Wales which flows principally westwards; draining to the sea into Tremadog Bay, south of Porthmadog.

The Dwyryd rises in the hills to the north of Ffestiniog. At its most northern extent, water draining from Moelwyn Mawr drains into the Tanygrisiau Reservoir, the outflow of which forms the source of the Afon Goedol. This is joined by the River Bowydd at grid reference: SH695438. Below Rhyd y Sarn, the river is joined by the Afon Cynfal which flows from the east down a deep wooded gorge which includes the spectacular Rhaeadr Cynfal (Cynfal waterfall) south of Ffestiniog. The main river from here on flows through a wide valley formed by glaciation but with a broad flat base formed from re-worked glacial moraines and riverine gravel deposits. The valley, the Vale of Ffestiniog, is worked for agriculture but is subject to routine winter flooding.

The Afon Tafarn-helyg has its confluence about one mile further downstream. This tributary rises south of Gellilydan just north of the reservoir of Llyn Trawsfynydd but does not receive any water from the reservoir.

...
Wikipedia