At a glance
Snowdon's dramatic copper-green crater lake at 600m — reached via the Miners' Track from Pen-y-Pass (2.5 miles, 400m ascent). Steeped in Arthurian legend. Free; Pen-y-Pass car park charged — use the Snowdon Sherpa bus in summer. LL55 4NU.
Safety information
Welsh mountains demand respect. Conditions can change in minutes — even Snowdon in July sees casualties from inadequate kit and unexpected weather.
Carry: waterproofs, walking boots, warm layer, hat & gloves, OS Explorer OL17 (Snowdonia) or OL18 (Harlech & Bala), 1.5 L water, charged phone, head torch. Check the weather at mwis.org.uk on the morning. In an emergency call 999, ask for Police / Mountain Rescue, give your what3words location. Local team: Llanberis Mountain Rescue Team.
About Llyn Glaslyn
Llyn Glaslyn — "the Green Lake" — sits in the great eastern cwm of Snowdon at approximately 600 metres above sea level, enclosed on three sides by the sheer headwall of the mountain. Its remarkable colour — a vivid blue-green caused by copper compounds dissolved from the surrounding volcanic rock — has drawn visitors and inspired legends for centuries.
The lake occupies the floor of a glacial cirque: a deep, bowl-shaped hollow carved by the glacier that once sat in this cwm, surrounded by near-vertical cliffs that rise to the summit ridge on the left (Yr Wyddfa, 1,085 m), the jagged Crib Goch ridge on the right, and the col of Bwlch y Saethau ("the Pass of Arrows") directly above. The scale of the surrounding rock architecture is overwhelming at close range.
Below Llyn Glaslyn, the larger Llyn Llydaw occupies the lower part of the cwm — its waters dramatically reflecting the Crib Goch ridge in calm conditions. Both lakes are served by the Miners' Track, the constructed path built in the 19th century to service the Britannia Copper Mine above Glaslyn. The track passes along Llyn Llydaw's northern shore on a causeway, then climbs more steeply to the upper lake. The ruins of the copper mine workings above Glaslyn are visible on the approach.
Find it on the map
Frequently asked questions
The most straightforward route to Llyn Glaslyn is the Miners' Track from Pen-y-Pass car park (LL55 4NU). The track follows a constructed path (originally built to serve the copper mines) for approximately 2.5 miles to the lake, gaining 400 metres of altitude. It is the most level of all Snowdon's approaches for most of its length — the gradient only increases significantly in the final section before the lake. Allow 1.5–2 hours uphill and 1–1.5 hours back.
Llyn Glaslyn's distinctive blue-green colour — its name means "green lake" in Welsh — is caused by copper compounds dissolved from the surrounding rock. Snowdon's eastern cwm was extensively mined for copper in the 19th century, and the mineral-rich water draining from the old workings gives the lake its vivid tint. The colour is most intense on cloudy days when the reflected sky doesn't wash out the green; in summer sunshine the lake appears a remarkable turquoise.
Llyn Glaslyn is associated with multiple strands of Arthurian mythology. One tradition holds that Excalibur — King Arthur's sword — was thrown into the lake after the Battle of Camlann (Arthur's last battle). Another legend places the Afanc — a water monster of Welsh mythology — in the lake. Arthur is also said to sleep in a cave beneath the cwm walls, awaiting Wales's hour of need. The lake's remoteness and dramatic setting make it a natural location for such stories.
Informal wild swimming in Llyn Glaslyn is practiced by those who reach it, but the lake is at 600 metres altitude and is cold year-round — even in August the water rarely exceeds 12°C. The altitude also means weather can change extremely quickly. If swimming, come prepared with a wetsuit, never swim alone, and be aware of the serious mountain environment you are in. Llyn Llydaw (slightly lower, 440m) on the Miners' Track below Glaslyn is also swum informally.
Yes — the Miners' Track passes the shore of Llyn Glaslyn before climbing steeply to the Bwlch y Saethau ridge and then joining the Pyg Track for the final push to the summit. Many walkers treat the lake as a natural rest stop on the way up. The view from the lakeshore — looking back down the cwm to Llyn Llydaw and across to the flanks of Crib Goch — is one of the classic Snowdon compositions.
The Britannia Copper Mine operated in the cwm around Llyn Glaslyn from the 1820s to the 1880s, extracting copper from the veins in the volcanic rock. At its peak the mine employed several hundred men. Ore was carried down the Miners' Track to the valley on the backs of mules. The mine ruins are visible on the slope above the lake, and the Miners' Track itself was built to serve the operation — hence its name and its unusually constructed, wide path compared to other Snowdon routes.