As water from a stream channel or surface runoff enters a wetland, the water spreads out and flows through dense vegetation. The velocity of the flow is reduced, allowing suspended material in the water to settle to the wetland surface. The roots of wetland plants can then bind the accumulated sediments. As much as 90 percent of the sediments that are present in runoff or in streamflow may be removed if the water passes through wetlands. Also, because pollutants, such as heavy metals, are attached to soil particles, the settling of sediments in wetlands further improves water quality.
