• A bay is a body of water partially surrounded by land. A bay is usually smaller and less enclosed than a gulf. The mouth of the bay, where meets the ocean or lake, is typically wider than that of a gulf.

    In naming bays and gulfs, people have not always made these distinctions. The Persian Gulf, for example, is much smaller than Hudson Bay, Canada.

    Bays can also be called lagoons, sounds, and bights. Lagos, the capital of Nigeria, is a bayside city. It sits on Lagos Lagoon, on the Bight of Benin, in the Gulf of Guinea, in the Atlantic Ocean.

    Bays form in many ways. Plate tectonics, the process of continents drifting together and rifting apart, causes the formation of many large bays.

    The Bay of Bengal, the largest bay in the world, was formed by plate tectonics. Millions of years ago, the Indian subcontinent crashed—and continues to crash—into the the massive Eurasian plate network. The Indian plate is subducting beneath the small Burma plate, forming the Sundra Trench. Because plate tectonics remain an active force in the Bay of Bengal today, the region is home to underwater earthquakes and tsunamis.

    Bays are also formed when the ocean overflows a coastline. Kowloon Bay, Hong Kong, was formed as the South China Sea overflowed the coastline of the Kowloon Peninsula. Today, Kowloon Bay has been almost entirely reclaimed from the sea. Kowloon Bay is a major industrial and financial area, and was home to Hong Kong's airport until a new facility was built in 1998.

    Another well-known coastal bay is New York Bay. New York Bay is actually two bays (Upper New York Bay and Lower New York Bay) connected by a strait called The Narrows. New York Bay is where the Hudson River meets the Atlantic Ocean.

    Many bays are formed as the coastline erodes into the ocean. Guanabara Bay, for example, was formed as the Atlantic Ocean eroded an inlet in South America. Today, Guanabara Bay, also known as the Harbor of Rio de Janerio, Brazil, is one of the Seven Natural Wonders of the World.

    A type of bay known as a ria is actually an estuary that has been taken over by the ocean. (An estuary is the mouth of a river.) Rias are often called "drowned rivers." Chesapeake Bay, on the East Coast of the United States, is one of the world’s largest rias. It is the drowned mouth of the Susquehanna River.

    Fjords are narrow bays formed by glaciers. A glacier slices through the bedrock of an area, leaving a long, steep canyon when it recedes. The sea seeps into the inlet, forming a fjord.

    Bays can also be found along the shores of lakes. Georgian Bay, for example, is a prominent bay in Lake Huron, one of North America’s Great Lakes. Georgian Bay is located in Ontario, Canada.

    Freshwater Bay is a bay on the Swan River, near the busy urban area of Perth, Australia. Freshwater Bay has been a center of trade and transportation along the river for centuries.

    Bay Ecosystems

    Bays have wildly diverse ecosystems. Large bays open to the ocean have marine habitats. Walker Bay, South Africa, is one of the most popular sites to view (and even dive with) great white sharks. Marine mammals such as els and southern right whales are also frequent visitors to Walker Bay.

    Bays on lakes and rivers have freshwater ecosystems. The wetlands of Georgian Bay, for example, are home to freshwater reptiles such as rattlesnakes and turtles. These species could never survive in a marine habitat.

    Most bays have brackish water. Brackish water has a greater salt content than freshwater, but not nearly as much as the ocean. Many species are uniquely adapted to brackish water. Oyster Bay, Tanzania, adopted the name of one of its most popular species.

    The Chesapeake Bay is so large that it features all three types of habitats. The northern part of the bay is almost entirely fresh. It is fed by the outflow of the Susquehanna River, and is home to species such as catfish, which favor freshwater habitats.

    The bulk of Chesapeake Bay is brackish. The outflow of rivers mix with the tidal waters of the Atlantic. The eastern oyster, one of the key aquaculture species of the area, thrives in brackish water.

    On the southern end of Chesapeake Bay, where it meets the Atlantic Ocean, the ecosystem is almost entirely marine. The blue crab, state crustacean of Maryland, is a mostly-marine species.

    Bays and People

    Bays are usually much calmer and more protected than seas or oceans. This makes them less likely to face severe damage from waves, tsunamis, and storm surges.

    Most bays make excellent harbors and major port cities are often located on them. Mumbai, India, sits on the mouth of the Ulhas River and the Arabian Sea. The bay at Mumbai, originally an archipelago, has been an important trading port between Europe and Asia for thousands of years. Mumbai, also known as Bombay, may have been named after the Portuguese saying for “good bay” (bom bahia), although there is no proof of this. Today, Mumbai is the second-largest city in the world and an important harbor for goods from the Middle East, East Asia, Africa, Europe, Australia, and the Americas.

    Some bays have been greatly altered by human activity. The geography of the San Francisco Bay has changed dramatically due to human activity in the 19th and 20th centuries, for instance.

    During the California Gold Rush of the 1850s and 1860s, miners in Northern California dumped tons of material into the rivers that empty into the San Francisco Bay. This material material included rocks and soil from mines, as well as chemicals used in the mining process. Eventually, all this material settled in parts of the bay. Wetlands and marshes replaced the freshwater habitats throughout the bay, and pollution increased.

    Industry in the 20th century has also changed the shape of the San Francisco Bay. Parts of the bay have been drained to create more land for housing and industry. Industries included salt evaporation ponds, mostly used to create material used in plastics and pharmaceuticals (drugs and medicines). Toxic chemicals used in the transportation industry were also manufactured on land reclaimed from the bay. San Francisco Bay is a strategic point in national defense, and the military has had naval and air stations there for almost a century.

    Pollution has altered the ecosystem of the bay, and introduced harmful chemicals into the bay, groundwater, and soil. Today, there are more than a dozen Superfund sites in and around San Francisco Bay. Environmentalists hope the government will restore the natural bay habitat.

    Chesapeake Bay

    People are trying to restore and protect Chesapeake Bay as well. The Chesapeake's importance as a center of commerce, transportation, and industry predates the Revolutionary War. Native Americans relied on the bay for fishing, trade, and communication long before that.

    Millions of people live on the Chesapeake Bay. The bay is anchored by the cities of Baltimore, Maryland, to the north and Norfolk, Virginia, to the south. In between, rural and urban areas dot the bay. Millions more people live in the Chesapeake's watershed, which includes more than a dozen rivers besides the Susquehanna, such as the Potomac, James, and York.

    Centuries of civilization have taken their toll. Chesapeake Bay has been polluted by sewage, wastes from industry, and runoff from chemicals used in agriculture. Parts of the Chesapeake Bay are occasionally "dead zones" where there is little life below the surface waters.

    Pollution and dead zones are not only bad for the environment. They also threaten the economy of the area. Maryland mussels and crabs are a major industry, harvested by fishermen called "watermen." Before the arrival of Europeans, the animals were a major source of food for Native Americans. However, due to overfishing and pollution in the bay, the number of animals is shrinking.

    Thousands of Maryland and Virginia watermen are working with environmental groups and local governments to monitor and restore the habitats of Chesapeake Bay. This ensures a healthy and profitable resource endures for future generations.

    Still, many remain worried about the future of Chesapeake Bay. One official, Lisa Jackson of the Environmental Protection Agency, worries. "If we come up short (in plans to clean up the bay), this may be the last generation of watermen on the Chesapeake Bay."

    A woman wearing a Hudson Bay Company coat points to a map of the Hudson Bay.

    Blink and You'll Miss It
    The enormous San Francisco Bay went practically undetected by explorers for 200 years. Spanish conquistadores began exploring the area in the mid-1500s, but the bay wasnt discovered until 1769. (Native Americans knew all about this rich natural resource. It was only "discovered" by Europeans.) Dozens and perhaps hundreds of ships sailed right past the bay. This happened for three reasons.

    First, even though the bay is huge, the opening to San Francisco Bay, the Golden Gate Strait, is very small. Even 21st-century cargo ships run aground or into bridges when trying to navigate the narrow opening.

    Second, the topography of the region gives an optical illusion when viewed from offshore. The islands of Alcatraz and Angel Island, inside the bay, can blend into the California Coastal Range on the far side of the bay, creating the illusion of an unbroken coastline.

    Third, and most important: San Francisco was, and remains, very, very foggy. Fog simply made the bay invisible to passing ships.

    Guantanamo Bay
    Guantanamo Bay is the largest bay on the southern side of Cuba, the largest island in the Caribbean Sea. Guantanamo Bay is a deep natural harbor that has tall, steep mountains separating it from the mainland of the island. The United States uses the isolated facilities at the Guantanamo Bay Naval Base to house high-risk prisoners at two detention camps: Camp Delta and Camp Iguana.

  • Term Part of Speech Definition Encyclopedic Entry
    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    aquaculture Noun

    the art and science of cultivating marine or freshwater life for food and industry.

    archipelago Noun

    a group of closely scattered islands in a large body of water.

    Encyclopedic Entry: archipelago
    bay Noun

    body of water partially surrounded by land, usually with a wide mouth to a larger body of water.

    Encyclopedic Entry: bay
    bedrock Noun

    solid rock beneath the Earth's soil and sand.

    Encyclopedic Entry: bedrock
    brackish water Noun

    salty water, usually a mixture of seawater and freshwater.

    canyon Noun

    deep, narrow valley with steep sides.

    Encyclopedic Entry: canyon
    civilization Noun

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

    Encyclopedic Entry: Key Components of Civilization
    commerce Noun

    trade, or the exchange of goods and services.

    continent Noun

    one of the seven main land masses on Earth.

    Encyclopedic Entry: continent
    crustacean Noun

    type of animal (an arthropod) with a hard shell and segmented body that usually lives in the water.

    dead zone Noun

    area of low oxygen in a body of water.

    Encyclopedic Entry: dead zone
    earthquake Noun

    the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

    economy Noun

    system of production, distribution, and consumption of goods and services.

    ecosystem Noun

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

    Encyclopedic Entry: ecosystem
    erode Verb

    to wear away.

    estuary Noun

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

    Encyclopedic Entry: estuary
    evaporation Noun

    process by which liquid water becomes water vapor.

    Encyclopedic Entry: evaporation
    fjord Noun

    long, narrow ocean inlet between steep slopes.

    Encyclopedic Entry: fjord
    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    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.

    groundwater Noun

    water found in an aquifer.

    Encyclopedic Entry: groundwater
    gulf Noun

    portion of an ocean or sea that penetrates land.

    Encyclopedic Entry: gulf
    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    harbor Noun

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

    Encyclopedic Entry: harbor
    Indian subcontinent Noun

    landmass in south-central Asia carried by the Indian tectonic plate, including the peninsula of India.

    industry Noun

    activity that produces goods and services.

    marine mammal Noun

    an animal that lives most of its life in the ocean but breathes air and gives birth to live young, such as whales and seals.

    marsh Noun

    wetland area usually covered by a shallow layer of seawater or freshwater.

    Encyclopedic Entry: marsh
    miner Noun

    person who excavates metal or other materials from the Earth.

    monitor Verb

    to observe and record behavior or data.

    mouth Noun

    place where a river empties its water. Usually rivers enter another body of water at their mouths.

    Encyclopedic Entry: mouth
    overfish Verb

    to harvest aquatic life to the point where species become rare in the area.

    pharmaceutical Noun

    drug or having to do with drugs and medications.

    plate tectonics Noun

    movement and interaction of the Earth's plates.

    pollution Noun

    introduction of harmful materials into the environment.

    Encyclopedic Entry: pollution
    port Noun

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

    Encyclopedic Entry: port
    profitable Adjective

    able to make money.

    recede Verb

    to retreat or withdraw.

    ria Noun

    low, wetland area near the mouth of a river. Rias are often called "drowned river valleys."

    runoff Noun

    overflow of fluid from a farm or industrial factory.

    Encyclopedic Entry: runoff
    seep Verb

    to slowly flow through a border.

    Seven Natural Wonders of the World Noun

    unscientific list of the most important or visually stunning natural geographic features on Earth.

    sewage Noun

    liquid and solid waste material from homes and businesses.

    storm surge Noun

    abnormal rise in sea level accompanying a hurricane or other intense storm. Also called a storm tide.

    Encyclopedic Entry: storm surge
    strait Noun

    narrow passage of water that connects two larger bodies of water.

    Encyclopedic Entry: strait
    strategic Adjective

    important part of a place or plan.

    subduct Verb

    to pull downward or beneath something.

    Superfund Noun

    federal program to clean up hazardous waste sites in the U.S. Also called the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA).

    toxic Adjective


    trade Noun

    buying, selling, or exchanging of goods and services.

    transportation Noun

    movement of people or goods from one place to another.

    tsunami Noun

    ocean waves triggered by an earthquake, volcano, or other movement of the ocean floor.

    urban area Noun

    developed, densely populated area where most inhabitants have nonagricultural jobs.

    Encyclopedic Entry: urban area
    watershed Noun

    entire river system or an area drained by a river and its tributaries.

    Encyclopedic Entry: watershed
    wetland Noun

    area of land covered by shallow water or saturated by water.

    Encyclopedic Entry: wetland