Wetlands occur naturally on every continent, except for Antarctica. The water in wetlands is either freshwater, brackish or saltwater.The main wetland types are classified based on the dominant plants and or the source of the water. For example, marshes are wetlands dominated by emergent vegetation such as reeds, cattails and sedges swamps are ones dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). Examples of wetlands classified by their sources of water include tidal wetlands (oceanic tides), estuaries (mixed tidal and river waters), floodplains (excess water from overflowed rivers or lakes), springs, seeps and fens (groundwater discharge out onto the surface), bogs and vernal ponds (rainfall or meltwater).Some wetlands have multiple types of plants and are fed by multiple sources of water, making them difficult to classify.

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