North Uist is the tenth largest Scottish island and the thirteenth largest island surrounding Great Britain. It has an area of 117 square miles (303 km2), slightly smaller than South Uist. North Uist is connected by causeways to Benbecula via Grimsay, to Berneray, and to Baleshare. With the exception of the south east, the island is very flat, and covered with a patchwork of peat bogs, low hills and lochans, with more than half the land being covered by water. Some of the lochs contain a mixture of fresh and tidal salt water, giving rise to some complex and unusual habitats. Loch Sgadabhagh, about which it has been said "there is probably no other loch in Britain which approaches Loch Scadavay in irregularity and complexity of outline", is the largest loch by area on North Uist although Loch Obisary has about twice the volume of water. The northern part of the island is part of the South Lewis, Harris and North Uist National Scenic Area, one of 40 in Scotland.