A long, narrow, wall-like structure extending out into a stream or lake from the bank or shore. Used to protect the bank from erosion. Also called a "wing dam" or "deflector." (Groins are often used with several in series to "train" the flow of a river around a bend where there is an erosion problem on the outside bank.) A bank or shore-protection structure in the form of a barrier oblique to primary motion of water, designed to control movement of bed material.