County Galway is famous for its numerous large lakes, including Lough Corrib, the largest lake in the Republic of Ireland, Lough Derg and Lough Mask. Most of it are lowlands, which are karstified Carboniferous limestone. With a high karst water level most karst features are water filled, and there are numerous depressions of glaciogene origin which are connected to the ground water and for karst lakes or turloughs. But the highlight of the county is definitely the Gort River lowland karst with its numerous sinks and resurgences. The river vanishes and reappears half a dozen times.