The islands are at relatively low altitudes, with central Ireland and southern Great Britain particularly low lying: the lowest point in the islands is Holme, Cambridgeshire at −2.75 m (−9.02 ft). The Scottish Highlands in the northern part of Great Britain are mountainous, with Ben Nevis being the highest point on the islands at 1,343 m (4,406 ft). Other mountainous areas include Wales and parts of Ireland, however only seven peaks in these areas reach above 1,000 m (3,281 ft). Lakes on the islands are generally not large, although Lough Neagh in Northern Ireland is an exception, covering 150 square miles (390 km2).[citation needed] The largest freshwater body in Great Britain (by area) is Loch Lomond at 27.5 square miles (71 km2), and Loch Ness, by volume whilst Loch Morar is the deepest freshwater body in the British Isles, with a maximum depth of 310 m (1,017 ft). There are a number of major rivers within the British Isles. The longest is the Shannon in Ireland at 224 mi (360 km).[citation needed] The river Severn at 220 mi (354 km)[citation needed] is the longest in Great Britain. The isles have a temperate marine climate. The North Atlantic Drift ("Gulf Stream") which flows from the Gulf of Mexico brings with it significant moisture and raises temperatures 11 °C (20 °F) above the global average for the islands' latitudes. Winters are cool and wet, with summers mild and also wet. Most Atlantic depressions pass to the north of the islands, combined with the general westerly circulation and interactions with the landmass, this imposes an east-west variation in climate.