Wetlands are areas of land where water covers the soil for most or all of the time. They provide flood control, improve water quality by filtering pollutants, and serve as important habitats. There are four main types of wetlands: marshes with shallow water and grassy plants, swamps with deeper water and woody trees and shrubs, and bogs and fens which are freshwater peatlands. Wetlands play key roles in flood control, coastal protection, groundwater recharge, sediment trapping, and intercepting pollution.