1. A jetty is a man-made structure that protrudes from land out into water. A jetty may serve as a breakwater, as a walkway, or both; or, in pairs, as a means of constricting a channel. The term derives from the French word jetée, 'thrown', signifying something thrown out. == For regulating rivers == === Wing dams === Jetties of one form, wing dams, are extended out, opposite one another, from each bank of a river, at intervals, to contract a wide channel, and concentrate the current to deepen the channel. === At the outlet of tideless rivers === Jetties have been constructed on each side of the outlet river of some of the rivers flowing into the Baltic, with the objective of prolonging the scour of the river and protecting the channel from being shoaled by the littoral drift along the shore. Another application of parallel jetties is in lowering the bar in front of one of the mouths of a deltaic river flowing into a tide — a virtual prolongation of its less sea, by extending the scour of the... from wikipedia.org