A harbor is a body of water sheltered by natural or artificial barriers. Harbors can provide safe anchorage and permit the transfer of cargo and passengers between ships and the shore. A harbor is deep enough to keep ships from touching bottom and should give ships and boats enough room to turn and pass each other.

Dredging keeps shipping channels deep and free of silt. Dredging is the process of removing sand and sediment from the bed of a body of water. This deepens and often cleans the body of water. The earthen material dredged from harbors can be used for nearby facilities, like larger beaches or stronger breakwaters (seawalls).

Most harbors are natural. They are located along many types of coastline. They occur in fjords, coves, and lagoons. They also occur along lakeshores and in estuaries, where rivers empty into larger bodies of water. The harbors in North America's Great Lakes, including Toronto, Canada (Lake Ontario), and Chicago, Illinois (Lake Michigan), remain some of the busiest for industrial ship traffic. Iron, steel, and timber are some of the raw materials shipped from manufacturing sites in the U.S. and Canada.

New York City has one of the world's finest natural harbors. The harbor has deep water, a small tidal range, and moderate currents. A small tidal range means that the water level is fairly consistent. There is little difference between high tide and low tide. Moderate currents mean movement of the water is predictable. This makes it easy for ships to maneuver, load and unload their cargo. Other cities with outstanding natural harbors are San Francisco, California; Rio de Janeiro, Brazil; and Sydney, Australia.

There are artificial harbors as well as natural ones. Breakwaters, huge walls of concrete, steel, and wire, are the most important element of artificial harbors. Breakwaters protect the harbor from storms and reduce the tidal range. The seabed in protected harbors is more likely to remain stable, although sediment from human activity is likely to accrete, or build up.

The harbor at Chennai, India, (formerly called Madras) relies on a series of artificial breakwaters. It is considered one of the finest artificial harbors in the world. Construction of the harbor began in the mid-1800s, and continued until the mid-1900s. Now, the busy harbor imports and exports such cargo as oil, cars, and consumer goods like clothes and software. The Chennai harbor also loads and unloads thousands of tourists, from throughout India, Australia, and the tropical islands of the Indian Ocean (like Maldives and Seychelles.)


Like Chennai, many harbors may serve as ports (manmade structures where ships load and unload cargo). For this reason, they are often vital to trade. When they function as ports, harbors often have artificial structures such as docks or jetties, as well as lighthouses, buoys, and other aids to navigation. The large size of modern vessels requires that harbors have deep ship channels.

Harbors have played an important role in civilization ever since people began using boats and ships at sea. Some 2,000 years ago, for instance, the Roman leader in what was then Palestine created a magnificent harbor at his city Caesarea Maritima. The ruins of this harbor, called Sebastos, are located on the Mediterranean Sea in present-day Israel. The Sebastos harbor relied heavily on breakwaters constructed from a unique form of concrete: a type of volcanic ash that hardened when mixed with seawater. These breakwaters at Sebastos were called moles.

Sebastos set a standard for future harbors. Most harbors were not improved until the mid-1800s. As commerce increased and ships grew bigger, enlarging and deepening harbors became necessary. Modern harbors range from small enclosures to huge commercial ports.

Harbors can be one of the most polluted ocean ecosystems. Human activity from both land and sea contribute to the pollutants. Because harbors are partially enclosed, the pollution has nowhere to go. It builds up in both the seawater and the sediment below. One source of pollution is ship discharge. This discharge can be anything from sewage and wastewater (used for cleaning) to chemical materials used for packing cargo. The cargo itself can break and spill into the water, releasing plastics, metals, and other toxic materials into the environment. Harbors often have to be dredged to clean up the accumulated waste and clear the channel for ships to pass through.

harbor
New York Harbor has ports in New York and New Jersey.

Mulberry Harbours
Mulberry Harbours were temporary, artificial harbors planned by military engineers from the United States and United Kingdom. (The U.K. spells the word harbour.) Mulberry Harbours were constructed for the Allied invasion of Europe during World War II. They were installed off the Atlantic beaches controlled by the Allies after D-Day, in Normandy, France.

Mulberry Harbours were more than breakwaters. They included docks for huge military transport ships, bridges, and more than 15 kilometers (10 miles) of roads. Mulberry Harbour cargo included tanks, jeeps, engineering supplies (like tents and tables), and food. The most important cargo unloaded at Mulberry Harbours, however, were millions of troop reinforcementssoldiers.

accrete
Verb

to build up or grow together.

accumulate
Verb

to gather or collect.

anchor
Verb

to hold firmly in place.

breakwater
Noun

a manmade wall rising from the sea floor that protects a harbor or beach from the force of waves.

buoy
Noun

floating object anchored to the bottom of a body of water. Buoys are often equipped with signals.

cargo
Noun

goods carried by a ship, plane, or other vehicle.

Noun

complex way of life that developed as humans began to develop urban settlements.

coastline
Noun

outer boundary of a shore.

commerce
Noun

trade, or the exchange of goods and services.

Noun

small inlet or bay in a larger body of water.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

discharge
Verb

to eject or get rid of.

dredge
Verb

to remove sand, silt, or other material from the bottom of a body of water.

Noun

community and interactions of living and nonliving things in an area.

Noun

mouth of a river where the river's current meets the sea's tide.

export
Noun

good or service traded to another area.

Noun

long, narrow ocean inlet between steep slopes.

Great Lakes
Noun

largest freshwater bodies in the world, located in the United States and Canada. Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior make up the Great Lakes.

Noun

part of a body of water deep enough for ships to dock.

import
Noun

good traded from another area.

industrial
Adjective

having to do with factories or mechanical production.

iron
Noun

chemical element with the symbol Fe.

Noun

structure protecting a harbor or inlet from a larger body of water.

Noun

shallow body of water that may have an opening to a larger body of water, but is also protected from it by a sandbar or coral reef.

lighthouse
Noun

structure displaying large, bright lights to warn and help ships navigate coastal waters.

magnificent
Adjective

very impressive.

maneuver
Noun

a skillful movement.

manufacturing
Noun

production of goods or products in a factory.

Noun

art and science of determining an object's position, course, and distance traveled.

oil
Noun

fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.

plastic
Noun

chemical material that can be easily shaped when heated to a high temperature.

pollutant
Noun

chemical or other substance that harms a natural resource.

pollute
Verb

to introduce harmful materials into a natural environment.

Noun

place on a body of water where ships can tie up or dock and load and unload cargo.

raw material
Noun

matter that needs to be processed into a product to use or sell.

seawall
Noun

barrier built to protect a beach or shoreline from erosion. Also called a bulkhead.

Noun

solid material transported and deposited by water, ice, and wind.

sewage
Noun

liquid and solid waste material from homes and businesses.

shelter
Noun

structure that protects people or other organisms from weather and other dangers.

shipping channel
Noun

deep waterway where large boats regularly transport goods and people.

Noun

small sediment particles.

software
Noun

electronic programs of code that tell computers what to do.

steel
Noun

metal made of the elements iron and carbon.

tidal range
Noun

the difference in height between an area's high tide and low tide.

timber
Noun

wood in an unfinished form, either trees or logs.

toxic
Adjective

poisonous.

trade
Noun

buying, selling, or exchanging of goods and services.

Noun

fragments of lava less than 2 millimeters across.

wastewater
Noun

water that has been used for washing, flushing, or industry.