Water may flow in one of two ways, either as laminar flow or turbulent flow. In very slow-moving streams the flow is often laminar and the water particles move in roughly straight line paths that parallel the stream channel. However, stream flow is usually turbulent, with the water moving in an erratic fashion that can be characterized as a swirling motion. Strong turbulent flow may exhibit whirlpools and eddies, as well as roiling whitewater rapids. Even streams that appear smooth on the surface often exhibit turbulent flow near the bottom and sides of the channel Turbulence contributes to the stream's ability to erode its channel because it acts to lift sediment from the streambed.