The islands are at relatively low altitudes, with central Ireland and southern Great Britain particularly low-lying: the lowest point in the islands is the North Slob in County Wexford, Ireland, with an elevation of . The Scottish Highlands in the northern part of Great Britain are mountainous, with Ben Nevis being the highest point on the islands at . Other mountainous areas include Wales and parts of Ireland, although only seven peaks in these areas reach above . Lakes on the islands are generally not large, although Lough Neagh in Northern Ireland is an exception, covering . The largest freshwater body in Great Britain (by area) is Loch Lomond at , and Loch Ness (by volume) whilst Loch Morar is the deepest freshwater body in the British Isles, with a maximum depth of . There are a number of major rivers within the British Isles. The longest is the Shannon in Ireland at . The river Severn at is the longest in Great Britain.