Lough Beagh is a stunning glacial lake nestled in the narrow Glenveagh valley of northwest County Donegal, Ireland, approximately 24 kilometres northwest of Letterkenny. Surrounded by the dramatic Derryveagh and Glendowan Mountains, steep granite cliffs rise on both sides of the lake to heights of around 300 metres (1,000 feet), creating a wild and remote setting that is as visually spectacular as it is productive for fishing. The lake measures approximately 6.5 kilometres long and 0.8 kilometres wide, with a surface area of 2.61 square kilometres and an average depth of 9.2 metres (30 feet). Situated entirely within Glenveagh National Park — the most northerly of Ireland's six national parks — Lough Beagh is fed primarily by the Owenbeagh River entering at its southern end and drains northward via the Owencarrow River, which connects it to its northern neighbour, Glen Lough. The underlying geology is predominantly granite, felsite, and other silica-rich intrusive rocks, giving the lake low alkalinity (less than 20 mg/l CaCO3), characteristic of wild, oligotrophic Irish upland waters. The lake features numerous small islands at its northern end, adding to both its scenic character and its fishing interest.