At a glance
A dramatic mountain lake on the A5 at the head of the Ogwen Valley — the starting point for Tryfan, the Glyderau and the Cwm Idwal National Nature Reserve. Free lake and paths; car park charged. Snowdon Sherpa bus stops here. LL57 3LZ.
About Llyn Ogwen
Llyn Ogwen sits at the head of the Nant Ffrancon pass at 300 metres above sea level — a shallow mountain lake just over a mile long, hemmed between the steep slopes of the Glyderau to the south and the Carneddau to the north. The A5 runs along its northern shore, and the Ogwen car park at the western end is the single most important mountain access point in Snowdonia: Tryfan's north ridge is 10 minutes' walk from here; the path to Cwm Idwal and the Glyderau starts from the same car park; the flanks of the Carneddau are accessible within the hour.
The lake itself is fed by the Afon Lloer descending from the cwm above and drains northwest into the Nant Ffrancon as the Afon Ogwen. Its maximum depth is only approximately 4 metres — far shallower than it appears from the road — and it supports typical upland lake species including brown trout. The surrounding ground is open access land managed under Natural Resources Wales.
Cwm Idwal, the glacial cirque above the lake, is a National Nature Reserve of major scientific significance. The Idwal Slabs — smooth, water-worn rock faces angled at around 30 degrees — are among the most famous rock climbing venues in Wales and the training ground for generations of British alpinists. The arctic-alpine plant community in the cwm includes species that are globally restricted to high-altitude environments and that survived here through the last Ice Age.
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Frequently asked questions
Llyn Ogwen is the starting point for some of the best mountain routes in Snowdonia. Tryfan (917 m) rises directly from the eastern shore — the North Ridge route starts from the A5 layby above the lake. The Glyderau range (Glyder Fawr 1,001 m, Glyder Fach 994 m) is accessed via the Cwm Idwal path (starts from the Ogwen car park). Y Garn (947 m) and Foel-goch are on the ridge above Cwm Idwal. All of these are serious mountain days requiring appropriate equipment and navigation ability.
Cwm Idwal is a glacial cirque (cwm) above Llyn Ogwen, accessible by a 30-minute path from the car park. It contains Llyn Idwal — a beautiful mountain lake — and is a National Nature Reserve protecting rare arctic-alpine plant communities that survived the last Ice Age here. Charles Darwin visited in 1831 and was one of the first to correctly interpret the cwm's glacial origin. The Idwal Slabs — smooth, inclined rock faces — are one of the most important rock climbing venues in Wales.
Llyn Ogwen is on the A5 road at the head of the Nant Ffrancon pass, approximately 5 miles from Bethesda and 12 miles from Betws-y-Coed. Use postcode LL57 3LZ for the Ogwen car park at the western end of the lake. The Snowdon Sherpa bus (seasonal) stops here, connecting to Bethesda and Capel Curig. The car park fills early on good weather weekends — arrive before 8am in summer.
Yes — the Ogwen Cottage Mountain Rescue base at the car park has a small café and toilet facilities, open seasonally. The café provides hot drinks and basic food — an important facility in a mountain area without other services. The Mountain Rescue base is staffed intermittently and manages rescues across the Glyderau and Carneddau ranges.
Wild swimming in Llyn Ogwen is practised informally but the lake is cold year-round (typically 10–15°C in summer) and has no formal swim provision. The lake is shallow at the western end and deeper toward the eastern end below Tryfan. The cold, clear water and mountain setting are exceptional, but standard wild swimming precautions apply — never alone, acclimatise gradually, use a wetsuit outside the warmest months.
The Nant Ffrancon is the valley that descends from Llyn Ogwen northwest toward Bethesda and the coast. It is one of the finest examples of a glacial trough in Britain — a straight, flat-floored valley flanked by steep mountain walls, formed when a glacier carved through the rock during the last Ice Age. Thomas Telford's A5 road follows the valley floor, and the views up the valley from below are a classic composition of mountain, lake and road.