Jetty

(1) On open seacoasts, a structure extending into a body of water to direct and confine the stream or tidal flow to a selected CHANNEL, or to prevent shoaling. Jetties are built at the mouth of a river or ENTRANCE to a BAY to help deepen and stabilize a CHANNEL and facilitate navigation.
(2) (SMP) A structure usually projecting out into the SEA at the mouth of a river for the purpose of protecting a navigational channel, a harbor or to influence water currents.