are swept by strong tides, and the Corryvreckan tide race between Scarba and Jura is one of the largest whirlpools in the world. Other strong tides are to be found in the Pentland Firth between mainland Scotland and Orkney, and the Grey Dog between Scarba and Lunga. There are also numerous clusters of islands in the Firth of Forth and the Firth of Clyde and in freshwater lochs such as Loch Lomond and Loch Maree. Outlying islands include St Kilda and Rockall the status of which is disputed. Scotland's islands have a varied topography. Mull, Skye and Arran are noted for their mountainous terrain, whilst Tiree and Coll are flat or low lying. Striking topographical differences can be seen within island groups themselves; in Orkney, the Island of Hoy is hillier and more rugged than surrounding islands and Harris is distinctive in being more mountainous than the islands of Lewis, North Uist, South Uist and Barra, in the Outer Hebrides. Islay's terrain is gentle and rolling; however, its neighbour Jura is mountainous and rugged. Rùm and Eigg display jagged terrain; nearby Canna and Muck are flatter. Rivers The ten major rivers of Scotland, in order of length, are: River Tay River Spey River Clyde River Tweed River Dee River Don River Forth River Findhorn River Deveron River Annan The watershed between river systems flowing west to the Atlantic Ocean and east into the North Sea is long. Lochs Fresh water bodies in Scotland are known as lochs, with the exception of the Lake of Menteith and one or two-man-made "lakes". 90% of the standing fresh water volume of Great Britain lies within Scotland. Loch Lomond is the largest freshwater body in Britain by area, although with a capacity of Loch Ness is the most voluminous. The water in Loch Ness is nearly double that of all the lakes of England and Wales combined, and is by volume the largest lake in the British Isles. Loch Lomond Loch Ness Loch Awe Loch Maree Loch Morar Loch Tay Loch Shin Loch Shiel Loch Rannoch Loch Ericht Distances to other countries Scotland's only land border is with England, and runs for approximately between the basin of the River Tweed on the east coast and the Solway Firth in the west. The Atlantic Ocean borders the west coast and the North Sea is to the east. The island of Ireland lies only from the