Lough Mask is one of Ireland's great western limestone loughs, covering approximately 22,000 acres in County Mayo and Galway in the province of Connacht. Stretching roughly 10 miles long by 4 miles wide, this formidable wild fishery is internationally recognized as one of the finest brown trout fisheries in Europe. Its crystal-clear waters are fed and filtered through the underlying limestone geology, and the lough is connected underground to the neighboring Lough Corrib to the south. The clarity and alkalinity of the water support rich invertebrate life, producing prolific hatches that sustain exceptional populations of wild brown trout. The nearest major angling town is Ballinrobe, though anglers base themselves at numerous villages around the lough's shores.