Afon Wnion is a top quality river with a memorable class IV narrow gorge section and a more relaxed lower section of class II with one class III-IV drop.
Although the initial section is fairly diminutive it soon grows with the confluence of various tributaries and gives some good, sustained class II with one small class III gorge.
Below Pont Llanrhaiadr the difficulty ramps up significantly with some big holes in high water, and then farther on some steep rapids as the river becomes more gorge-like. The walls of the gorge then close in even more and deliver an exciting and atmospheric rollercoaster ride.
Due to the tightness of the gorge section the potential for blockages and strainers is ever present.
The lower section of the Wnion provides a very fine class II run (with one class III to IV drop) down to the confluence with the Mawddach.