Llyn Trawsfynydd

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Llyn Trawsfynydd is a large artificial reservoir near the village of Trawsfynydd in Gwynedd, North Wales. It covers about 4.8 square kilometres (roughly 1,200 acres), a little larger than Bala Lake.

The lake was created between 1924 and 1928 by building four dams to supply water for the Maentwrog power station. More than twenty properties, including the farms Brynhir and Llwynderw, were lost to make the lake. A small road along the western shore and a footbridge were built to help people avoid long detours.

In 1965 the lake began supplying cooling water for the Trawsfynydd nuclear power station, which started generating electricity for the UK grid. To increase the water volume, one dam was rebuilt in the early 1960s because the nuclear plant needed water and the Maentwrog plant had used most of it. The nuclear power station was shut down in 1991, and decommissioning began, planned to finish in 2083. Since then, the lake has returned to natural water levels and wildlife has recovered, while it is still used for hydroelectric power generation. The lake has an average depth of about 4 metres.