At a glance
Llyn Cowlyd (LL26 0LP) — the largest lake in the Conwy area, at 390 m below the Carneddau moorland. 2-mile walk in from Trefriw. Wild swimming (very cold · remote · experienced only). Trefriw served by bus 19. Free. Water supply reservoir — swim only, don't access dam infrastructure.
About Llyn Cowlyd
Llyn Cowlyd is a long, finger-shaped lake at 390 m on the southern flank of the Carneddau — the largest and deepest lake in the Conwy county area, dammed at its north-eastern end for water supply. The approach from Trefriw climbs through Gwydyr Forest and onto open moorland before reaching the dam — a walk of approximately 2 miles and 350 m of ascent. The lake stretches south-westwards below Pen Llithrig y Wrach and Craig yr Isfa, its dark waters reflecting the high Carneddau ridges above.
The character of Llyn Cowlyd is more austere than the dramatic glacial cwm lakes of the Snowdon and Ogwen areas — this is moorland rather than mountain architecture, the lake lying in a broad upland bowl rather than a knife-edged corrie. That gives it a particular solitude: on a midweek day in early autumn, when the summer crowds have dispersed, the lake is often entirely deserted. The water is cold and clear — maintained as a water supply reservoir by Dŵr Cymru Welsh Water, it is kept to a high standard. Wild swimming is legally permitted under open access land provisions.
Safety information
Wild swimming carries serious risks. Never swim alone. Tell someone where you're going and when you'll be back. Enter the water gradually to avoid cold-water shock. Know your exit point before you start. Wear a tow float and consider a wetsuit even in summer — Welsh lake and sea temperatures rarely exceed 16°C.
In an emergency call 999 and ask for the Coastguard (sea) or Police / Mountain Rescue (lakes & rivers). Nearest A&E: Ysbyty Gwynedd, Penrhosgarnedd, Bangor LL57 2PW. Tel: 01248 384 384.
Find it on the map
Frequently asked questions
The most common approach to Llyn Cowlyd is from Trefriw village (LL27 0JZ) in the Conwy Valley, via a forestry track and then open moorland path that climbs approximately 350 m over 2 miles to the dam at the lake's north-eastern end. An alternative approach is from Dolgarrog (south of Trefriw) via the Coedty reservoir and then uphill to the lake. Trefriw is served by Arriva bus 19 from Llandudno, Conwy, and Llanrwst. The Conwy Valley Railway (Blaenau Ffestiniog–Llandudno Junction) serves Llanrwst station, approximately 2 miles from Trefriw. The walk to the lake takes approximately 1–1.5 hours from Trefriw.
Llyn Cowlyd's appeal lies in its combination of size, relative remoteness, and position — a long, dark-watered lake stretching beneath the moorland ridges of the Carneddau, with Pen Llithrig y Wrach (754 m) and Craig yr Isfa rising above the far shore. The lake is substantially larger than most Snowdonia wild swimming lakes, giving room to swim distances. The water is cold and clear (it is a water supply reservoir, maintained to a high standard). The moorland approach through Gwydyr Forest and onto the open plateau above has a wild character distinct from the more glacially dramatic Snowdonia cwm lakes. The lake sees fewer swimmers than the more accessible Ogwen and Llanberis lakes.
Llyn Cowlyd is a cold, remote mountain lake at 390 m — wild swimming carries real risks. The water is very cold, particularly outside July and August. The 2-mile walk-in means that any emergency is a significant distance from help. As with all mountain wild swimming in Wales: never swim alone, tell someone your exact plan and expected return time, enter the water gradually to avoid cold water shock, and know your exit point before entering. Llyn Cowlyd is a water supply reservoir managed by Dŵr Cymru Welsh Water — access to the lake itself is generally permitted under open access land provisions, but the dam and reservoir infrastructure should not be accessed. The nearest A&E is Ysbyty Gwynedd, Bangor LL57 2PW, tel: 01248 384384.
Yes — Llyn Cowlyd is one of the access points for the southern Carneddau. From the lake, paths ascend to Pen Llithrig y Wrach (754 m) to the west and Craig yr Isfa to the north-west, from where the main Carneddau ridge (Carnedd Llewelyn at 1,064 m, Carnedd Dafydd at 1,044 m) can be reached. This makes a long and serious mountain day of 10+ miles suitable only for experienced walkers with navigation ability. Craig yr Isfa's north face is one of the major rock climbing crags in the Carneddau, and the view from the ridge above the lake is outstanding. For day visitors to the lake who are not mountain walkers, the moorland immediately around the lake gives pleasant walking without requiring full mountain equipment.
The moorland above Trefriw and around Llyn Cowlyd supports upland bird species including red grouse (common on the heather), meadow pipit, and skylark. In summer wheatear and ring ouzel are present. The lake itself holds brown trout — it is managed as a fishing lake, with permits required for fishing (wild swimming does not require a permit). Ravens are regular over the moorland. In the Gwydyr Forest section on the approach to the lake, common woodland birds include treecreeper and crossbill. The Conwy Valley below Trefriw is one of the better locations in North Wales for red kite, which can often be seen soaring above the valley.