Best Wild Swimming Spots in Snowdonia & Gwynedd
Written by UK Hidden Gems Editorial
Updated 5 August 2026
The best wild swimming spots in Snowdonia & Gwynedd are Llyn Cau, Cwm Pennant, Rhaeadr Du, Llyn Gafr, Llyn Llagi, Llyn y Gadair and Llyn Cwmorthin.
Snowdonia and Gwynedd hold their swimming water high in the mountains, in dark corrie lakes scooped by ice and quiet pools among old slate ruins. Cadair Idris alone holds four of these: the deep, cliff-ringed Llyn Cau on its southern side, and Llyn Gafr, Llyn y Gadair and the smaller lakes strung along the paths up its northern flanks, dark and cold in their rocky hollows.
Below the Cnicht ridge, the round, deep Llyn Llagi sits under a steep back wall of crag, and above Blaenau Ffestiniog the natural Llyn Cwmorthin lies among the ruins of a notorious slate quarry. In the quarry country of Cwm Pennant a clear pool waits high among the workings, and at Ganllwyd the twin black falls of Rhaeadr Du drop through an ancient oak wood.
Most are reached on a mountain walk rather than a stroll, and the water stays cold whatever the season. Here are seven wild swimming spots to seek out across Snowdonia and Gwynedd.
Llyn Cau
Photo: Andrew Wood via Geograph.org.uk
Llyn Cau is a lake sitting in a deep rock hollow beneath the summit of Cadair Idris, ringed on three sides by the high walls of Craig Cau. It is a classic glacial corrie lake, its water dark and clear.
The Minffordd Path climbs to it from the car park to the south, a good pull uphill past falls and pools, before carrying on around the rim of the crag toward the top of the mountain. A small stony beach on one side draws walkers and swimmers.
Old stories tell of the lake being bottomless.
Cwm Pennant
Photo: Ceri Thomas via Geograph.org.uk
Cwm Pennant is a quiet valley in the hills of Snowdonia, near Garndolbenmaen, with the young Afon Dwyfor running down it. The slopes carry the ruins of old slate quarries, and a clear pool high in the valley among the workings draws wild swimmers.
It is an informal spot, without any facilities, set in remote hill country. The valley runs green and steep-sided below the higher peaks.
Rhaeadr Du
Photo: Mike Parker via Geograph.org.uk
Rhaeadr Du, the black waterfall, is a twin cascade on the Afon Gamlan in oak woodland at Ganllwyd, at the edge of the Coed y Brenin forest in Gwynedd. It takes its name from the dark slab of rock it pours over, and drops in two stages of some sixty feet through a National Trust nature reserve of ancient trees.
A short circular walk of about two miles from a car park leads to a viewing point, up a stone stairway, on paths that are slippery when wet. Near the bridge stands a rock carved with a line of old verse.
Llyn Gafr
Photo: Jeremy Bolwell via Geograph.org.uk
Llyn Gafr, the goat lake, is a small mountain lake on the northern side of Cadair Idris. It sits on the Fox's Path, one of the steeper and looser ways up the mountain, below the larger Llyn y Gadair higher up.
Most walkers pass it on the way up or down rather than making it the goal. It lies in a rocky hollow among the crags, quiet and little written about, with no path around it or any facilities.
Llyn Llagi
Photo: Peter S via Geograph.org.uk
Llyn Llagi is a mountain lake in central Snowdonia, set in a rocky hollow below the Cnicht ridge, north of the Nantmor valley. Nearly round and deep, it sits under a steep back wall of crag that climbers and scramblers use.
Walkers reach it on foot as a detour from the Cnicht route, following paths in from the narrow lane. It is a remote and quiet spot, ringed by rough moorland and rock.
Llyn y Gadair
Photo: Michael Graham via Geograph.org.uk
Llyn y Gadair is a lake in a rocky hollow below the summit of Cadair Idris, on the northern side of the mountain. It sits along the Pony Path, one of the main routes to the top, in a bowl beneath steep crags, and is a favourite spot for a rest or a wild camp on the way up.
Its water is dark and cold. This is a different lake from the deeper Llyn Cau on the southern side, which is the one tied to the mountain's bottomless-lake stories.
Llyn Cwmorthin
Photo: Bill Harrison via Geograph.org.uk
Llyn Cwmorthin is a natural lake in a hanging valley above Tanygrisiau, near Blaenau Ffestiniog, set among the ruins of the Cwmorthin slate quarry. A track climbs to it from the village, leading past broken barracks where the quarrymen lodged, spoil heaps, and the roofless shell of the workers' chapel.
The quarry here had such a poor safety record that it earned a grim nickname among the miners. Work began early in the nineteenth century and finally stopped in 1997.
The lake and the wrecked buildings around it make it a much-photographed walk.
FAQs
Which mountain in Snowdonia has the most swimming lakes?
Cadair Idris holds several. The deep, cliff-ringed Llyn Cau sits in its corrie on the southern side, reached by the Minffordd Path, while Llyn Gafr and Llyn y Gadair lie along the steeper northern routes, the Fox's Path and the Pony Path, dark and cold in their rocky hollows.
Are any wild swimming spots in Snowdonia linked to old slate quarries?
Two are. Llyn Cwmorthin lies in a hanging valley above Blaenau Ffestiniog among the ruins of a slate quarry once notorious for its safety record, with broken barracks and a roofless chapel around it, and Cwm Pennant holds a clear pool high among old quarry workings.
What is Rhaeadr Du at Ganllwyd?
Rhaeadr Du, the black waterfall, is a twin cascade on the Afon Gamlan at Ganllwyd, dropping some sixty feet in two stages over a dark slab of rock through a National Trust reserve of ancient oak woodland. A short circular walk of about two miles leads to a viewing point up a stone stairway.
Conclusion
Snowdonia and Gwynedd keep their swimming water up in the mountains, cold and dark in the hollows the ice left behind. Cadair Idris holds a cluster of it, from the deep, cliff-ringed Llyn Cau on the south to Llyn Gafr and Llyn y Gadair on the northern paths.
Below Cnicht, the round Llyn Llagi sits under its crag, and above Blaenau Ffestiniog the natural Llyn Cwmorthin lies among the ruins of a notorious slate quarry, as does the clear pool high in Cwm Pennant. At Ganllwyd, the twin black falls of Rhaeadr Du drop through an ancient oak wood.
Most are reached on a mountain walk and stay cold whatever the season, so go prepared. These are the wild swimming spots to seek out across Snowdonia and Gwynedd.
