Trawsfynydd nuclear power station is a former Magnox nuclear power station situated in Snowdonia National Park in Gwynedd, Wales. The plant, which became operational in 1965, was the only nuclear power station in the UK to be built inland, with cooling water that was taken from the artificial Llyn Trawsfynydd reservoir which also supplies the hydro-electric Maentwrog power station. It was closed in 1991. Its ongoing decommissioning by Magnox Ltd was expected to take almost 100 years, but in 2021 the Welsh government arranged for the power station to be redeveloped using small-scale reactors.