A groin is a straight structure that is perpendicular to the shore, constructed with stone, sheet pile or similar material to stabilize a stretch of beach against erosion. Groins function only when sand is moving in the nearshore area. Groins create or build out a sandy beach that then acts as a wave dissipation zone. Groins can be constructed either singly or in a series (as shown). A saw-toothed shaped shoreline is created with a series of groins.