Wetlands are dynamic landforms which vary in both time and space. Tanzania's wetlands are classified according to the physiography and the environment in which they exist. Coastal wetlands, Rift System wetlands and the wetlands of highland drainage basins are the major groups. Coastal wetlands are formed by wave action and tidal influence; beaches and lagoons exist because of wave action; mudflats, marshes, mangrove swamps, estuaries and deltas are tidal in origin. Rift System wetlands occur in the rift depressions and are characterised by salt lakes, playas, swamps and short streams with inland drainage. The highlands are drained by long rivers originating in the inland catchments and ending in oceans or lake basins. On the way to their outlets, they form lakes, swamps and floodplains. Wetlands occur due to a combination of high rainfall and the tropical climate of Tanzania which favours processes such as meandering of rivers and the formation of floodplains. The morphogenesis of Tanzania's wetlands is related not only to local processes but also to regional factors such as climate, tectonism and the eustatic sea level changes which occurred in the past.