Bays, Gulfs, and Straits

Bays, gulfs, and straits are types of waterbodies that are contained within a larger body of water near land. These three waterbodies are usually located at important points of human activities; thus, conflicts with nature and neighbors can result.

An infrared photograph of the San Francisco Bay area, taken from the space shuttle Discovery, shows the bay's shape and the heavy development in the region.
An infrared photograph of the San Francisco Bay area, taken from the space shuttle Discovery, shows the bay's shape and the heavy development in the region.


A bay is a small body of water or a broad inlet that is set off from a larger body of water generally where the land curves inward. The San Francisco Bay, off the coast in northern California, is a well-known bay in the United States. Examples of other bays include the Bay of Pigs (Cuba), Hudson Bay (Canada), Chesapeake Bay (Maryland and Virginia), and Bay of Bengal (near India).

Bays usually occur on oceans, lakes, and gulfs, and generally not on rivers except when there is an artificially enlarged river mouth. An example of a bay at a river's mouth is New York Bay, at the mouth of the Hudson River.

Health of Bays.

All bays are important to the continued health of the surrounding environment . However, these bays can be degraded when the water's natural state is changed by the introduction of foreign materials into water flowing into the bay, or into the bay itself. For instance, the San Francisco Bay is connected to the Sacramento–San Joaquin Delta estuary , which is the largest estuary on the west coast of the United States. This aquatic system supports more than 120 species of fish and is a waterfowl migration and wintering area.

Although known for its natural beauty and importance to the health of its surrounding area, the San Francisco Bay has been degraded by many human activities such as commerce and recreation. For example, more than 95 percent of the tidal marshes along the shore have been filled. Large reductions (and in some cases losses) in fish and wildlife habitat have resulted. The flow of fresh water into the estuary and the delta also has been reduced due to diversion of the water by pumps within the delta, thereby increasing the estuary's salinity.


A gulf is a large body of water, sometimes with a narrow mouth, that is almost completely surrounded by land. It can be considered a large bay. The world's largest gulf is the Gulf of Mexico, with a total surface area of about 1,554,000 square kilometers (600,000 square miles). It is surrounded by Mexico, the southern coast of the United States, and Cuba, and contains many bays, such as Matagorda Bay (Texas) and Mobile Bay (Alabama). Examples of other gulfs include the Gulf of California, Gulf of Aden (between the Red Sea and the Arabian Sea), and the Persian Gulf (between Saudi Arabia and Iran). The Persian Gulf is important with respect to world energy because petroleum is transported through its waters in oil tankers.


Scientific investigations of the Gulf of Mexico have documented a large area off the coast of Louisiana with depleted oxygen levels, a condition known as hypoxia. Most aquatic species cannot survive at such low oxygen levels, and a so-called "dead zone" results. After the 1993 flood of the Mississippi River, this area of hypoxia more than doubled in size, to over 18,000 square

This satellite view of the Arabian Peninsula illustrates gulfs, a strait, and marginal seas. The narrow Strait of Hormuz (center right) connects the Persian Gulf (interior) and the Gulf of Oman (far right), which joins the Arabian Sea (bottom right). The Red Sea (and the Gulf of Aden) is at the bottom left.
This satellite view of the Arabian Peninsula illustrates gulfs, a strait, and marginal seas. The narrow Strait of Hormuz (center right) connects the Persian Gulf (interior) and the Gulf of Oman (far right), which joins the Arabian Sea (bottom right). The Red Sea (and the Gulf of Aden) is at the bottom left.
kilometers (6,950 square miles). Generally, hypoxia can be traced back to excessive nutrients and excessive growth of algae , which ultimately dies and whose massive decay reduces the concentration of oxygen needed for aquatic species.

Because of its enlarged size and continuing existence, the hypoxic zone could threaten the economy of the U.S. Gulf of Mexico region, including its highly valued commercial and recreational fisheries. Like bays, gulfs are important measures of the health of aquatic ecosystems because so many waterbodies drain into them. Whatever has been deposited into these waterbodies eventually can reach gulfs.


A strait is a narrow passageway of water, usually between continents or islands, or between two larger bodies of water. The Strait of Gibraltar is probably the world's most famous strait. It connects the Atlantic Ocean on its west with the Mediterranean Sea on its east. It also separates northern Africa from the Rock of Gibraltar on the southernmost point of the Iberian Peninsula. Historically, almost all commerce between the Mediterranean Sea and Atlantic Ocean was routed through the Strait of Gibraltar. It is still an important route of international trade.

Two other well-known straits are the Strait of Bosporus and the Strait of Hormuz. The Strait of Bosporus is located in southwestern Asia and southeastern Europe. It connects the Black Sea (from the north) and the Sea of Marmara (from the south), and splits northwestern Turkey. The Strait of Hormuz is located at the southeastern end of the Persian Gulf (see photograph on page 70). It is a narrow waterway that can be (and has been) controlled to prevent ships from sailing through the gulf.

Choke Point.

When a body of water such as a strait is capable of being blocked or even closed in order to control transportation routes, the body is called a "choke point." Historically, the Strait of Gibraltar has been one of the world's most important choke points. However, the Strait of Hormuz has become an important choke point in recent years because of increasing Middle East tensions. The Strait is surrounded by the United Arab Emirates and Oman (on one side) and Iran (on the other side). Hormuz connects the Persian Gulf to the Arabian Sea and ultimately to the Indian Ocean.

SEE ALSO Chesapeake Bay ; Estuaries ; Islands, Capes, and Peninsulas ; Marginal Seas ; Transportation .

William Arthur Atkins


March, William M. Environmental Geography: Science, Land Use, and Earth Systems, 2nd ed. New York: John Wiley & Sons, 2002.

Strahler, Alan H. Introducing Physical Geography, 3rd ed. New York: John Wiley & Sons, 2003.

Internet Resources

Guantanamo Bay Naval Base and Ecological Crises. Trade and Environmental Database (TED). <> .

Access USGS—San Francisco Bay and Delta. United States Geological Survey. <> .

Hypoxia in the Gulf Of Mexico. Gulf of Mexico Hypoxia Assessment, National Ocean Service, National Oceanic and Atmospheric Administration. <> .

Rabalais, Nancy N. Hypoxia in the Gulf Of Mexico. NOAA Coastal Services Center, National Oceanic and Atmospheric Administration. <> .


Guantánamo Bay is a sheltered inlet within the Caribbean Sea, located in southeastern Cuba near the city of Guantánamo. During the SpanishAmerican War in 1898, the United States gained access to the outer harbor of Guantánamo Bay. Through an agreement signed with Cuba in 1903, the United States obtained the right to maintain a naval base at Guantánamo Bay. In 1934, a treaty reaffirmed the U.S. right to lease the site. The treaty gave the United States a perpetual lease on Guantánamo Bay, and may only be rescinded if the United States should abandon the area or by the mutual consent of Cuba and the United States.

About 18,390 hectares (45,440 acres) of water (32 percent), solid ground (49 percent), and swampland (18 percent) comprise Guantánamo Bay U.S. Naval Base, a complex of airfields and repair, supply, and training facilities. The base is strategically important because of the maritime route between the United States and Central and South America, and its close proximity to the Panama Canal.


Scientists believe that during its past, the Strait of Gibraltar has closed periodically, stopping the flow of water between the Mediterranean Sea and Atlantic Ocean. Water that today flows into the Mediterranean Sea from the Atlantic Ocean usually remains in the Mediterranean for between 80 to 100 years before returning to the Atlantic.

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