Llyn Celyn is a substantial reservoir nestled in the heart of Gwynedd, Wales, formed by the flooding of the Tryweryn valley between 1960 and 1965. Sitting at an elevation of 299 metres above sea level, this mid-altitude water body stretches roughly 2.5 miles long by 1 mile wide, covering approximately 320 hectares (790 acres). The reservoir plays a vital role in the regional water management system, working in conjunction with Llyn Tegid and Llyn Brenig to regulate the flow of the River Dee and maintain water supplies for communities including Llangollen, Wrexham, Chester, and Merseyside. Characterised by low alkalinity and humic water chemistry — typical of upland Welsh reservoirs — Llyn Celyn offers a rugged, scenic fishing environment set against the dramatic landscapes of North Wales.