A jetty is a long, narrow structure that protects a coastline from the currents and tides. Jetties are usually made of wood, earth, stone, or concrete. They stretch from the shore into the water.

Currents and tides of an ocean can gradually wash away a beach or other features along the coastline. This is called erosion. Strong river currents or waves from a lake can also erode a coastline. Jetties protect the shoreline of a body of water by acting as a barrier against erosion from currents, tides, and waves.

Jetties can also be used to connect the land with deep water farther away from shore for the purposes of docking ships and unloading cargo. This type of jetty is called a pier.

Jetties can be popular tourist attractions. They usually provide safe access to coastal areas. The Swakopmund jetty in the African country of Namibia was constructed with iron in 1905 in order to protect the towns harbor from gathering too much silt, or sediment. This jetty was renovated in 2006 and is popular with tourists because of the view it offers of Namibias coastline.

The most famous jetty is probably Spiral Jetty, a large sculpture created by the artist Robert Smithson in 1970. Spiral Jetty is on the northeast shore of the Great Salt Lake, in the U.S. state of Utah. Smithson constructed the 4,500 457-meter (1,500-foot) jetty out of rock and earth. Its unusual shape twists in a circular, counter-clockwise direction.