Lakes are also common along slow-moving rivers and in low areas near the sea. Portions of meandering rivers that are separated from the main river become isolated lakes known as oxbows . Tectonic lakes occur in natural fissures. An example is Lake Tanganyika, which fills a depression in Africa s Great Rift Valley a region where the continent is being pulled apart. Groundwater may even dissolve limestone to form underground lakes.
Lakes can also form in volcanic calderas.
Among the most famous crater lakes is Oregon s Crater Lake. Ocean currents may deposit sediments along a shoreline, cutting off bays which then become coastal lagoons . Many artificial lakes have been created as sources of hydroelectricity, water for irrigation and other uses. Lakes are like animals in that they are born, grow, then die. Some lakes disappear when their source of water is diminished.