Short, sharp river out of Llyn Padarn under Yr Wyddfa, through Caernarfon and into the Menai Strait. The Seiont is the salmon and sea-trout backbone of a wider three-river system with the Gwyrfai and Llyfni; Arctic char persist in the catchment in Llyn Cwellyn. Quick to rise, quicker to fall — Eryri spate logic in compact form. Slate and schist bedrock underlie this river. Atlantic salmon are under serious conservation pressure — Natural Resources Wales mandates catch-and-release for salmon on all rivers, so all fish must be returned.
The Seiont drains Llyn Padarn at the foot of the Llanberis pass and runs north-west out of the heart of Eryri to the Menai Strait at Caernarfon — known in its uppermost reach, above Llanrug, as the Afon Rhythallt. It is a short, lively river of clear, cold, acidic water off the highest ground in Wales, carried over hard rock and slate-strewn gravel through the old quarry country beneath Snowdon. The system is a nursery for migratory fish: salmon and sea trout run up through Llyn Padarn, and the lake itself holds Arctic charr, a relic of the last ice age. Hydro works block the way above Padarn, so fish reach the upper catchment through a two-kilometre tunnel cut beneath the mountain. The character is spate-fed and quick. Wading is rock-and-slate work, uneven and slick in places, the river rising fast after rain on the tops.
Wading: Slick slate underfoot, fast to rise
Summer-autumn runs (June–September), primarily nocturnal
- Slate
- Partly confined
- Pool riffle
- Step pool
