The Great Rivers and Lakes of the World

Rivers and lakes shape civilisations. The Nile, at about 6,650 kilometres, is conventionally cited as the world's longest river, flowing north through north-eastern Africa to the Mediterranean, though some recent studies argue the Amazon may be longer depending on how its source is measured. The Amazon, in South America, is the world's largest river by discharge, carrying more water than the next several largest rivers combined, and draining a rainforest basin of about 7 million square kilometres. The Yangtze in China is Asia's longest river, the Mississippi–Missouri system drains much of North America, and the Danube flows through more countries than any other river, linking central and eastern Europe.

Lakes are also unevenly distributed. The Caspian Sea, despite its name, is the world's largest lake by area, a landlocked saltwater body between Europe and Asia. Lake Baikal in Siberia is the world's deepest lake and holds about a fifth of the world's unfrozen surface fresh water. The African Great Lakes, including Victoria, Tanganyika and Malawi, are major sources of fish, water and transport, and also sites of political tension over shared resources. In North America, the Great Lakes form the largest group of freshwater lakes by area and a major shipping route between the United States and Canada.

Rivers and lakes are rarely contained within one country. About 40 per cent of the world's people live in river basins shared by two or more countries, so sharing water, managing floods and controlling pollution are international tasks. The Nile basin, shared by eleven countries, the Indus basin, shared by India and Pakistan among others, and the Mekong basin in South-East Asia all show how upstream dams, irrigation and diversions affect downstream neighbours. Agreements, joint commissions and, where they fail, disputes and courts are the normal tools for managing shared waters.

For civil studies, great rivers and lakes are a lesson in interdependence. A dam built upstream changes water, silt, fisheries and power downstream; a polluted lake affects drinking water, health and livelihoods across borders; and a drying lake, such as the Aral Sea, shows how irrigation choices can destroy an entire ecosystem and economy. Geography therefore leads directly to diplomacy: water is at once a natural resource, an economic input and a political relationship.