Northern Ireland was covered by an ice sheet for most of the last ice age, the legacy of which can be seen in the extensive coverage of drumlins in Counties Fermanagh, Armagh, Antrim and particularly Down. Occupying just over 17% of the island of Ireland, Northern Ireland is certainly crisscrossed by uplands and low mountains, but its most prominent and arguably its most valuable landform is Lough Neagh, the largest freshwater lake in the United Kingdom and one of the largest in western Europe. As for those mountains, the major ranges include the Sperrin, Mourne, and the Antrim Plateau that stretches along its northeastern coastline. Slieve Donard in the Mourne Mountains of the south is its highest point, rising to 850 meters.