From the deck of the Nautical Mile
Water covers over 70% of the Earth’s surface, yet not all bodies of water are named the same. From oceans to rivers, lakes to lagoons, each type of water body has a unique classification based on size, depth, location, and connectivity to other water sources. Understanding why these distinctions exist can provide insight into geography, ecology, and human usage of water.
Sounds
A sound is a large sea or ocean inlet, often connecting two larger bodies of water or lying between the mainland and an island. Sounds can be formed through glacial activity or rising sea levels, creating deep waterways ideal for navigation. Examples include the Puget Sound in Washington State, and locally, Pine Island Sound.
Bays
A bay is a broad inlet of water where the land curves inward, often forming a protected harbor. Bays are typically connected to oceans or seas and provide ideal conditions for fishing, boating, and trade. San Francisco Bay and the Bay of Bengal are well-known examples.
Oceans
Oceans are the largest bodies of saltwater on Earth, covering vast expanses and separating continents. There are five main oceans—Atlantic, Pacific, Indian, Arctic, and Southern—each connected to one another, forming a global system of water circulation. Oceans are defined by their immense size, depth, and influence on climate patterns and marine ecosystems. The Pacific is our largest ocean with 60,000,000 square miles. Atlantic comes in at #2 with 41,000 sq miles of water.
Seas
Seas are smaller than oceans but still contain saltwater and are typically partially enclosed by land. They are often connected to an ocean, influencing tides and marine life. Examples include the Mediterranean Sea, which is nearly surrounded by Europe, Asia, and Africa, and the Caribbean Sea, bordered by North and South America. The largest sea is the Philippine Sea with 2,199,000 square miles of water.
Lakes
Lakes are inland bodies of water, usually freshwater, that are larger and deeper than ponds. They can be natural or man-made, formed by glacial activity, tectonic movements, or damming. Famous lakes include Lake Superior in North America and Lake Baikal in Russia, the deepest freshwater lake in the world.
The Caspian is the world's largest inland body of water. Because of its size and depth, it’s described as both a sea as well as the world's largest lake. Its 143,000 sq miles of water borders Kazakhstan, Russia, Turkmenistan, Azerbaijan, and Iran. The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not freshwater: the 1.2% salinity classes it with brackish water bodies. It contains about 3.5 times as much water, by volume, as all five of North America's Great Lakes combined. The color of the Caspian darkens from north to south, thanks to changes lake in depth and perhaps sediment and other runoff. The northern part of the lake is just 16 to 20 feet deep. The southern end, however, plunges more than 3,300 feet.
Ponds
Ponds are smaller, shallower bodies of water, typically with still or slow-moving water. Unlike lakes, ponds often support more plant life across their entire surface due to their shallow depth. They are common in wetlands and serve as habitats for amphibians, insects, and aquatic plants.
Lagoons
Lagoons are shallow bodies of water separated from a larger body, such as an ocean or sea, by a barrier like a coral reef or barrier island. They are often found in coastal regions and can be saltwater or brackish. The famous Blue Lagoon in Iceland is an example of a geothermal lagoon with mineral-rich waters.
Rivers
Rivers are flowing bodies of freshwater that move from higher elevations to lower areas, often emptying into a larger water body such as an ocean, sea, or lake. They can vary in size, from small streams to massive waterways like the Amazon or the Mississippi. Rivers are essential for transportation, agriculture, and ecosystems.
Blue Hole
A blue hole, which in its own way is a large body of water, is a large underwater sinkhole or vertical cave, typically found in coastal or oceanic regions. These formations are characterized by their striking deep blue color, which contrasts sharply with the lighter, shallower waters surrounding them. This coloration results from the depth and clarity of the water, which absorbs most colors of the light spectrum except for blue.
Blue holes form when limestone bedrock is eroded by water over thousands or even millions of years, creating massive caverns that eventually collapse and become submerged. They can be found in both marine and inland locations, with some of the most famous examples being the Great Blue Hole in Belize, Dean’s Blue Hole in the Bahamas, and the Dragon Hole in the South China Sea.
These underwater sinkholes often contain unique ecosystems, with limited oxygen levels at deeper depths, supporting unusual marine life and even ancient fossils. They are popular among divers and scientists due to their mysterious depths, biodiversity, and geological significance. Some blue holes can reach depths of over 1,000 feet, making them among the deepest known sinkholes on Earth.
Bights
A bight is a broad, shallow indentation in a coastline, larger than a bay but with a more gradual curve. Bights are typically characterized by calmer waters and serve as natural harbors. The Great Australian Bight is a significant example along the southern coast of Australia.
Each type of water body plays a unique role in shaping landscapes, ecosystems, and human civilization. Understanding these distinctions enhances our appreciation of the world’s diverse aquatic environments.
Fjord
A fjord is a deep, narrow, and elongated sea or lake inlet with steep cliffs or slopes, typically formed by the glacial erosion of a valley. Fjords are usually found in regions with a history of glaciation, such as Norway, Canada, New Zealand, and Chile. They are often U-shaped in cross-section and can extend far inland, sometimes with branching tributaries. Many fjords have deep waters, making them navigable for ships, and they often feature stunning natural landscapes with waterfalls, forests, and towering rock formations.
Straight
A strait is a narrow body of water that connects two larger bodies of water, often serving as a crucial passage for marine navigation. Straits can form naturally due to geological activity, erosion, or rising sea levels, and they often play significant roles in trade, geopolitics, and ecosystems. Some well-known examples include the Strait of Gibraltar, which connects the Atlantic Ocean to the Mediterranean Sea, and the Bering Strait, which separates Russia and Alaska while linking the Pacific and Arctic Oceans. Due to their strategic importance, many straits have been historically contested and remain vital to global commerce and transportation today.
Gulf
A gulf is a large body of water that is partially enclosed by land but has a wide opening to a larger sea or ocean. It is typically bigger and deeper than a bay and often formed by tectonic activity, erosion, or rising sea levels. Gulfs can have strategic and economic importance, serving as key locations for ports, trade, and marine life.
Basin
A basin is a geographical depression where water collects, typically surrounded by higher land. In the context of a body of water, a basin usually refers to the natural or artificial area that holds and directs water flow. Some common examples include river basins, ocean basins, and lake basins.
