River buildup is a natural process that occurs when sediment, such as SILT, accumulates in a river. SILT is a type of soil particle that is very fine and can be easily carried by water. When SILT accumulates in a river, it can cause the river to become shallower and wider, which can lead to flooding. The buildup of SILT can also reduce the amount of oxygen in the water, which can be harmful to aquatic life.