A jetty is any of a variety of structures used in river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

, dock

Dock (maritime)

A dock is a human-made structure or group of structures involved in the handling of boats or ships, usually on or close to a shore.However, the exact meaning varies among different variants of the English language...

, and maritime

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

 works that are generally carried out in pairs from river banks, or in continuation of river channels at their outlets into deep water; or out into docks, and outside their entrances; or for forming basin

Dock (maritime)

A dock is a human-made structure or group of structures involved in the handling of boats or ships, usually on or close to a shore.However, the exact meaning varies among different variants of the English language...

s along the sea-coast for port

Port

A port is a location on a coast or shore containing one or more harbors where ships can dock and transfer people or cargo to or from land....

s in tide

Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

less seas. The forms and construction of these jetties are as varied as their uses (directing currents

Ocean current

An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...

 or accommodating vessels), for they are formed sometimes of high open timber-work, sometimes of low solid projections, and occasionally only differ from breakwater

Breakwater (structure)

Breakwaters are structures constructed on coasts as part of coastal defence or to protect an anchorage from the effects of weather and longshore drift.-Purposes of breakwaters:...

s in their object.