Riparian buffers are generally an area of trees, shrubs or other vegetation along a stream or waterway that buffers the influx of pollutants such as sediment to improve the health of the stream, river or lake. The plants help filter pollutants that would otherwise enter waterways. Buffers help reduce land erosion and sediment delivery to streams or sedimentation, which can be harmful to stream health. Although erosion and sedimentation are natural processes, inappropriate land-use can accelerate their impact and cause sediment pollution. A floodplain is an area next to a waterway that serves to hold and infiltrate excess water from heavy rains. It allows sediment to settle out of floodwaters. Building on floodplains and attempts to keep water out of the floodplains only exacerbates flooding in other areas and forces more stormwater into stream channels, leading to greater streambank erosion. Wetlands absorb and slow floodwaters. They also absorb excess nutrients, sediment and other pollutants before they reach streams, rivers, and lakes or estuaries. Some of the most important wetlands are only seasonally wet.