Large woody debris (LWD) are the logs, sticks, branches, and other wood that falls into streams and rivers. This debris can influence the flow and the shape of the stream channel. Large woody debris, grains, and the shape of the bed of the stream are the three main providers of flow resistance, and are thus a major influence on the shape of the stream channel. Some stream channels have less LWD than they would naturally because of removal by watershed managers for flood control and aesthetic reasons.