At a glance
Large upland reservoir in southern Snowdonia dominated by the decommissioned Trawsfynydd Nuclear Power Station — lakeside circuit walk (6–7 miles), trout fishing (permit required), Rhinog mountains access, and a striking industrial-wild landscape. Harlech 7 miles. LL41 4TL.
About Llyn Trawsfynydd
Llyn Trawsfynydd is a reservoir created in the 1920s in the upland plateau between the Rhinog mountains and the Moelwyn range in southern Eryri, covering over 3 square miles of former moorland and farmland. The lake feeds the Maentwrog hydroelectric scheme in the valley below, and was used from 1965 to 1991 as the cooling source for Trawsfynydd Nuclear Power Station — the only inland nuclear power station ever built in Britain, designed by Sir Basil Spence on the eastern shore. The station was decommissioned after 1991 and its twin reactor buildings, still prominent above the lake shore, give the landscape an unusual quality: concrete modernist architecture against the ancient Rhinog ridgeline, reflected in the still water of the reservoir.
The lake is one of the better fishing venues in southern Snowdonia — stocked with brown and rainbow trout, with a shoreline circuit path giving access to bank fishing from designated areas. Boat fishing is available. The village of Trawsfynydd, on the eastern shore, is the birthplace of the poet Hedd Wyn (Ellis Humphrey Evans, 1887–1917), who was posthumously awarded the Chair at the 1917 National Eisteddfod after being killed on the Western Front — the "Black Chair" ceremony is one of the most poignant moments in Welsh cultural history. A statue in the village square commemorates him.
The Rhinog mountains — some of the roughest and most demanding hill terrain in Wales — are accessible from the western shore. Rhinog Fawr (720 m) is 4 miles west; the access track passes through a landscape of boulder fields, heather, and ancient Bronze Age trackways. Harlech Castle and its beach are 7 miles west. Blaenau Ffestiniog and the Ffestiniog Railway are 9 miles north on the A470.
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Frequently asked questions
Llyn Trawsfynydd is an artificial reservoir created between 1923 and 1928 by damming the Afon Prysor to supply water to the Maentwrog hydroelectric power station 4 miles downstream in the Dwyryd Valley. The construction required the flooding of significant areas of upland farmland and the displacement of farming communities — a pattern repeated across Snowdonia in the 20th century. The reservoir became the cooling source for Trawsfynydd Nuclear Power Station, built on the eastern shore in the early 1960s and operational from 1965 to 1991, when it was the only inland nuclear power station in Britain. The power station was decommissioned after 1991 and is now undergoing a long-term decommissioning process managed by Magnox Ltd.
The Trawsfynydd Nuclear Power Station is not open to the public — it is an active decommissioning site managed by Magnox Ltd and access is restricted to site personnel. The twin reactor buildings are, however, highly visible from the lake shore and the surrounding roads, and the site has an unusual presence in the landscape: its concrete structures, reflected in the lake, have become an inadvertent landmark in an otherwise wild mountain setting. Architectural historians have noted that the station was designed by Sir Basil Spence (architect of Coventry Cathedral) to fit sympathetically into the landscape — an intention that is debated but at least acknowledges the visual challenge.
Yes — Llyn Trawsfynydd is one of the better fishing lakes in southern Snowdonia, stocked with brown and rainbow trout. The warm water from the nuclear station's cooling operations (now cooling, as the station is decommissioned) historically produced unusually large trout — fish of several pounds were regularly caught. Fishing permits are available from local tackle shops and from the lake's fishing club. Boat fishing is available on parts of the lake; bank fishing is permitted from designated areas. The season runs approximately April to October.
The lake has a circuit path around its shoreline — a 6-7 mile walk with views across the water to the power station and the Rhinog mountains to the west. The circuit uses public footpaths and access land around the reservoir perimeter; some sections are rough and require good walking footwear. The village of Trawsfynydd is on the eastern shore — the poet Hedd Wyn (Ellis Humphrey Evans, killed in the First World War before being posthumously awarded the National Eisteddfod chair, the "Black Chair") was from the village and is commemorated by a statue in the village square. The Rhinog mountains, accessible from the western shore, provide more demanding mountain walking.
Trawsfynydd village is on the A470 trunk road between Dolgellau (12 miles south) and Blaenau Ffestiniog (9 miles north), in the upland plateau between the Rhinog mountains and the Moelwyn range. It is within Eryri National Park. The Ffestiniog Railway passes through Blaenau Ffestiniog 9 miles north; Harlech Castle is 7 miles west on the coast. The village is also near the start of the Rhinog Fawr access track — the Rhinogs are some of the roughest and most demanding mountains in Snowdonia, offering serious hillwalking for those prepared for trackless terrain.