Humans make changes to stream systems by building dams along the river courses.
Building a dam will decrease the velocity of flow. Immediately behind the dam, where the lake is formed, the slope of the river is essentially reduced to zero. These changes result in the deposition of sediment. Lakes that are formed behind dams must often be dredged because of this velocity decrease and deposition. Downstream from the dam the sediment load is zero, and the slope is increased.