Dams can change how sediment moves in rivers. Scientists studied a dam in Vermont using a special tracer called 7 Be. They found that sediment behind the dam moves downstream quickly. The sediment moves at a steady speed, even when the water flow changes. The dam affects sediment transport for about 1 kilometer downstream. Beyond that, new sediment replaces what gets trapped by the dam. The dam also affects the types of bugs living in the riverbed, with more caddisflies found downstream of the dam.