Afon Dwyryd rises in the hills north of Blaenau Ffestiniog, gathering the small mountain streams of the slate country — the Goedol, the Teigl, the Cynfal — and runs down through a steep wooded valley to the broad sand flats of Traeth Bach, the estuary it shares with the Glaslyn south of Porthmadog. It is a spate river off ancient Cambrian and Ordovician rock, the water clear and acidic, quick to colour and rise with the heavy rain of the Ffestiniog hills. The old slate quarries loom over its headwaters. The Dwyryd carries runs of sea trout — sewin — and salmon up off the tide on the floods, with wild brown trout in the upland tributaries. The character is steep, rocky, wooded freestone falling to a wide tidal estuary. Wading is rock-and-boulder work, slick and uneven, and the river rises fast off the mountain after rain.

Wading: Slick rock, fast to rise off the mountain