Reservoirs are artificial lakes, produced by constructing physical barriers across flowing rivers, which allow the water to pool and be used for various purposes. The volume of water stored in reservoirs worldwide is estimated to be 4,286 km3 (Groombridge and Jenkins, 1998).
Wetlands include swamps, bogs, marshes, mires, lagoons and floodplains. The 10 largest wetlands in the world by area are: West Siberian Lowlands (780,000-1,000,000 km2), Amazon River (800,000 km2), Hudson Bay Lowlands (200,000-320,000 km2), Pantanal (140,000-200,000 km2), Upper Nile River (50,000-90,000 km2), Chari-Logone River (90,000 km2) Hudson Bay Lowlands in the South Pacific (69,000 km2), Congo River (40,000-80,000 km2), Upper Mackenzie River (60,000 km2), and North America prairie potholes (40,000 km2) (Pidwiny, 1999). The total global area of wetlands is estimated to be 2,900,000 km2 (Groombridge and Jenkins, 1998). Most wetlands range in depth from 0 to 2 m. Estimating the average depth of permanent wetlands to be about 1m, the global volume of wetlands could range between 2,300 km3 and 2,900 km3.