At a glance
Llyn Cwellyn (LL54 6TN) is a large lake below Snowdon near Rhyd Ddu — free access, NRW car park at Rhyd Ddu. Start of the Rhyd Ddu Path to Snowdon (1,085m). Outstanding photography location (Snowdon reflections). No swimming (water supply reservoir). Welsh Highland Railway station adjacent. 5–6 mile full circuit; short flat sections near village.
About Llyn Cwellyn
Llyn Cwellyn occupies the valley between the western flanks of the Snowdon massif and the Nantlle Ridge — a position that gives it some of the most dramatic mountain scenery around any lake in Wales. The full Snowdon ridge from Yr Aran through the main summit to Llechog is visible from the eastern shore; the seven summits of the Nantlle Ridge form the western horizon. On still mornings both are reflected in the lake surface with extraordinary clarity.
The lake is a water supply reservoir managed by Dŵr Cymru (Welsh Water), meaning that swimming is not permitted — but this does not diminish its value as a walking and photography destination. The lakeshore path on the east side is open and follows the water's edge for most of its length, giving changing perspectives on the mountains above as you walk. The northern end of the lake at Rhyd Ddu has a good car park (NRW), toilet facilities and the station for the Welsh Highland Railway.
For walkers, Llyn Cwellyn is primarily the approach to Snowdon via the Rhyd Ddu Path — one of the quietest and most rewarding routes to the summit. But the lake is worth a visit in its own right, particularly for those who appreciate mountain photography or simply want a peaceful lake walk without the crowds of Llanberis.
Find it on the map
Frequently asked questions
Llyn Cwellyn lies on the western flank of Snowdon, in the valley between the Snowdon massif and the Nantlle Ridge, approximately 5 miles south-east of Caernarfon. The village of Rhyd Ddu is at the northern end of the lake on the A4085 road. The NRW car park at Rhyd Ddu (LL54 6TN) is the main access point — it is also the station for the Welsh Highland Railway, which stops here on its run between Caernarfon and Porthmadog.
A full circuit of the lake is a pleasant walk of approximately 5–6 miles, taking 2–3 hours. The east shore has a clear track (part of the approach to Snowdon via the Rhyd Ddu path); the west shore path is rougher and less well-defined but gives the best views back across the lake to the Snowdon ridges. The northern end by Rhyd Ddu has a flat, accessible section suitable for shorter walks.
Llyn Cwellyn is one of the finest photography locations in Snowdonia — particularly on still mornings when the surface is mirror-calm and the Snowdon ridges and Nantlle peaks reflect in the water. The lake faces east, making morning the optimal time for reflected mountain light. The Welsh Highland Railway crossing near the northern end adds a foreground subject for train photography.
Yes — the Rhyd Ddu Path to Snowdon (1,085m) starts from the car park at Rhyd Ddu at the northern end of the lake. The path climbs the western ridge of Snowdon via Llechog, joining the main summit ridge below the peak. It is one of the quieter Snowdon routes and arguably the most dramatic in terms of views — overlooking the Nantlle Ridge and the Llŷn Peninsula as you ascend. Distance approximately 8km return, ascent 900m, allow 5–7 hours.
Yes — Llyn Cwellyn is a water supply reservoir serving the Caernarfon area, managed by Dŵr Cymru (Welsh Water). This means that swimming in the lake is not permitted (unlike nearby Llyn Padarn which is open for swimming). The lake is approximately 1.8 miles long and 50 metres deep. Despite its reservoir status, it retains a completely natural appearance and the lakeshore walk is open and free.