Rivers and Lakes Scotland is characterized by an abundance of streams and lakes (lochs). Notable among the lakes, which are especially numerous in the central and northern regions, are Loch Lomond (the largest), Loch Ness, Loch Tay, and Loch Katrine. Many of the rivers of Scotland, in particular the rivers in the west, are short, torrential streams, generally of little commercial importance. The longest river of Scotland is the Tay; the Clyde, however, is the principal navigational stream, site of the port of Glasgow. Other chief rivers include the Forth, Tweed, Dee, and Spey. More than 2 per cent of the Scottish land surface is covered by over 27,000 lochs and more than 50,000 km of rivers and burns. Fresh waters represent a more significant landscape feature in Scotland than in any other part of Britain. In fact, 91 per cent of the volume of standing fresh water in Great Britain is within Scotland. Management of water is of crucial importance to our daily lives and to Scotland's biodiversity. A number of priority species are associated with freshwater habitats. Some, like the reed beetle, have very specific habitat requirements. Others, like the otter, are highly mobile, moving between different types of aquatic habitat. Running waters are characterised by having an obvious direction of flow. They change gradually in character (size, substrate, plants and animals) from source to mouth. Erosion is a characteristic effect of running water, and materials so removed may be transported considerable distances. As a further consequence of erosion and deposition, most running waters increase the length of their channels with age, as both cutting back to the source and meandering on the flood plain proceed. Scotland has about two-thirds (950) of the main river systems in Great Britain.