A careful examination of the lakes of the world will reveal their immense human significance. In countries where they are found in abundance, such as Finland, Canada, U.S.A ., Sweden and the East African States, lakes, together with other inland waterways, have played a dominant role in the human, economic, social and cultural life of the people. The pattern of settlement, commerce and communication is very closely related to the distribution of the water features.
The following are major uses of lakes:
1) Means of communication: Large lakes like the Great Lakes of North America provide a cheap and convenient form of transport for heavy and bulky goods such as coal, iron, machinery, grains and timber. The Great LakesSt. Lawrence waterways penetrate more than 2740 km (1700 miles) into the interior. They are thus used as the chief arteries of commerce. It is estimated that the annual tonnage passing through the Sault-Ste. Marie Canal, or the Soo Canal/ between Lake Huron and Lake Superior, is greater than the combined annual tonnage Of the Suez and Panama Canals.
2) Economic and industrial development: Early settlements and town sites were very much influenced by the presence of lakes. Lakes, are an even more decisive factor when they are drained by large rivers with outlets to the sea. The Great Lakes-St. Lawrence waterways were responsible for the development of the interior wheat farms and lakeside industries. Raw materials, minerals and fuels were economically handled and assembled in the ‘HOMES’ district (Lake Huron, Ontario, Michigan, Erie and Superior), which has since become one of the greatest industrial districts in the world. Similarly, Lakes Poyang, Tung Ting and other lakes of the central Yangtze basin have greatly assisted in the commercial and industrial development of Wuhan (Wuchang, Hanyang and Hankow).
3) Water storage: Lakes of either natural or artificial origin are vital sources of domestic water supply to surrounding towns and industrial cities. For example, in Britain Lake Thirlmere supplies water to Manchester, Loch Katrine to Glasgow, Lake Vyrnwy (in Wales) to Liverpool. The MacRitchie Reservoir supplies Singapore and the Ayer Itam Dam supplies Penang.
4) Hydro electric power generation: In mountainous districts, lakes or man-made reservoirs are used to furnish a good head of water to generate hydroelectric power. Natural lakes are preferred to artificial reservoirs because the volume of water that flows from them varies very little throughout the year. For instance, the Niagara River, flowing from Lake Erie to Lake Ontario, has a very regular supply of water for its power stations, whereas the Catawba River in the Carolinas, which does not flow from a lake, has very little water during the dry season. Cotton mills have been forced to close down during the period of drought due to insufficient power supplies to run the mills. The Aswan Dam on the Nile in Egypt and the Lloyd Barrage on the Indus at Sukkur suffer from similar defects. Apart from the High Aswan Dam, other large dams in Africa include the Akosombo Dam in Ghana, the Kainji Dam in Nigeria and the Kariba Dam of Zambia-Zimbabwe on the River Zambezi in Central Africa. The Abu Bakar Dam of the Cameroon Highlands supplies much hydro-electricity for central West Malaysia.
5) Agricultural purposes: As mentioned earlier most lakes will eventually be eliminated and when they dry up, their former beds will be covered with thick layers of fertile alluvium. They make excellent agricultural land like the fertile Vale of Pickering in Yorkshire or the rich Red River Valley of Canada, which was in fact the former site of Lake Agassiz.
Modern multi-purpose dams, besides generating hydroelectric power, also supply water for irrigation, e.g the Sennar Dam on the Blue Nile in Sudan, the Burrinjuck Dam on the Murrumbidgee in Australia, and the Ghulam Mohammed Barrage on the Indus in West Pakistan. The Sansanding Barrage in Mali, West Africa, was primarily built to supply water for the irrigation of the dead Inland delta of the Niger.
6) Regulating river flows: A river with large lakes in its basin, seldom experiences serious floods or lack of water. By absorbing the excess Neater during heavy rain, a lake reduces the effects of serious flooding downstream. In the dry season, it releases its water so that a steady flow of the river is maintained. Because lakes retain part of the sediment load, rivers that are leaving lakes have clearer water. Lakes that have such functions include the Poyang and Tung Ting on the Yangtze Kiang, Tonle Sap on a tributary of the Mekong and Lake Constance on the upper Rhine. Where such lakes are not available and flooding is a serious problem, artificial reservoirs are constructed e.g. the Hoover Dam on the River Colorado and the Bhakra and Nangar Dams on the Sutlej in India. One of the secondary aims of building the Kainji Dam (Nigeria) is to control the frequent annual floods along the Niger Valley; another is the possibility of farming the fadama or the Niger Valley all the year round, under controlled flow and irrigation.
7) Moderation of climate: Large and deep lakes which are heated more slowly than the land by day and cooled more slowly than the land by night, exercise an appreciable effect in moderating the climate of a region in the same way as oceans affect adjoining land-masses. Water in the lakes cools the air in summer, by absorbing part of the heat and warms it in winter by releasing the heat. For example, the eastern shores of Lakes Erie, Ontario and Huron have a much milder winter than those of the west, because the on-coming breezes are warmed and early frosts are minimized. This part of the Lake Peninsula is therefore important for grapes and fruit farming. Large lakes like Lake Michigan and the Caspian Sea also exert some influence on the cloudiness and precipitation of the region. Their large expanse of water acts almost like part of the ocean, and helps to precipitate atmospheric moisture into rain. The leeward side of Lake Michigan records a little more precipitation than the windward side, though the actual amount is often not easily noticeable. Small lakes have practically no effect at all on either temperature or rainfall.
8) Source of food: Many large lakes have important supplies of protein food in the form of fresh-water fish. Sturgeon is commercially caught in the Caspian Sea, salmon and sea trout in the Great Lakes, and in Tonle Sap, in the Khmer Republic, fishing is a leading occupation. Amateur fishermen have found fishing in lakes and rivers a most rewarding pastime. In many countries, artificial lakes have been created for inland fish breeding. This is particularly important in China and Japan.
9) Source of minerals: Salt lakes provide valuable rock salts. In the Dead Sea, the highly saline water is being evaporated and produces common salt, almost indispensable for human well-being. Borax is mined in the salt lakes of the Mojave Desert.
Gypsum is mined in Cheshire, and Stassfurt, a small distance from Berlin. It is very rich in potash and other chemical deposits which have given rise to a wide range of chemical industries formed in an earlier geological period.
10) Tourist attraction and health resorts: Some of the world’s best frequented holiday and health resorts are located on lakesides; for example, Lake Geneva, Lake Lucerne, Lake Lugano, Lake Como, Lake Placid (New York), Lake Vaner and Lake Vatter (Sweden), the English Lake District and Taiping Lakes. The glacier formed lakes of the Alps have made the tourist industry a national occupation of the Swiss. The artificial lakes created by the Akosombo Dam (Ghana) and Kainji Dam (Nigeria) are fast attracting holiday makers. The Kainji lake has the advantage of the nearby Borgu Game Reserve.