Filling in wetlands often results in increased flooding, both downstream, by speeding water along, or upstream, by blocking water flow. Erosion and Sedimentation Control - Wetlands vegetation helps to filter sediment by decreasing water velocity. Suspended particles settle in the wetland and do not enter navigational channels, lakes, and reservoirs. In much the same manner, wetlands also help prevent erosion of shorelines and valuable agricultural land by serving as buffers between wave or stream activity and adjacent lands. Chemical processes in the soil also immobilize chemicals and heavy metals.
Water leaving a wetland is frequently cleaner than water entering the wetland.
Wetlands also protect fresh groundwater supplies in coastal areas by preventing saltwater intrusion. Recharging Groundwater Supplies - Wetlands sometimes are helpful in recharging groundwater. This function is especially important where groundwater is the sole-source of drinking water or constitutes the major source of usable water. Maintaining Surface Flows - Wetlands frequently serve as groundwater discharge sites, thereby maintaining the quality and quantity of surface water supplies. Fish and Wildlife Habitats - Many species of fish and wildlife depend on wetlands for critical parts of their life cycle.