What’s the Difference Between a Gulf and a Bay?

The Earth is 71% water. With that much liquid sloshing around, people have invented many terms to describe different bodies of water. There are gulfs and bays, but also ponds, lakes, seas, channels, and dozens of other water-based geographical features. With so many different names, how can you tell them apart? Here’s the difference between a gulf, a bay, and just about any other body of water.

Gulf

Long pier on beach at sunset
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A gulf is a body of water surrounded by land, much like a bay. Gulfs and bays share the same basic definition, but there are some slight nuances between the two. The main difference between a gulf and a bay is size. Gulfs are typically (though not always) much larger than bays. They’re also characterized by small openings and round bodies. The Gulf of Mexico is the largest gulf in the world.

Bay

Bay with boats scattered throughout and large rock formations
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A bay is also defined as a body of water surrounded by land. Bays are generally smaller than gulfs, although that’s not always the case. The world’s largest bay, the Bay of Bengal in India, is actually bigger than the world’s largest gulf. Typically, though, bays have a wider opening than gulfs in comparison to the rest of the body of water.

Pond

Pond with water lillies and grass all around
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Lakes and ponds are two other bodies of water that get confused because, like gulfs and bays, they share a definition. Ponds and lakes are standing or slow-moving bodies of water. Beyond that, there’s really no official difference between the two. Lakes are typically larger than ponds, but the term “larger” is subjective. Areas that don’t have much standing water might consider one body of water to be a lake, while in a wetter area it would be considered a pond.

The Great Pond in Maine, for example, is one of the largest ponds in the world at more than 13 square miles, and is much larger than many lakes. Maine happens to have a lot of ponds and lakes, so 13 square miles to the people who live there isn’t really that big.

Lake

Blue lake surrounded by trees with island in middle and mountains in distance
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Lakes are slow-moving or standing bodies of water, just like ponds. They're generally considered the larger of the two, and while there are no official standards to determine the difference between a lake and a pond, there are some unofficial ones. The following three conditions may help determine if a body of water is a lake:

  • Light doesn’t reach the bottom at the deepest point
  • It has the capacity to make waves up to one foot in height
  • Temperature varies throughout

If all three are true, then the body of water is most likely a lake. Again, though, there’s no official definition, so this might not always be the case.

Sea

Clear blue water off the beach in the Caribbean Sea
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Seas are also large bodies of water. To be considered a sea, a body of water must be made of saltwater, connected to the ocean, and located at sea level. Seas are typically much larger and deeper than lakes.

In some cases, though, bodies of water are named seas but are actually lakes. For instance, the Dead Sea is technically a lake because it’s landlocked and located below sea level. The Caspian Sea is also landlocked and isn’t connected to the ocean, but it’s so big that it earned the title of “sea” anyway. It’s technically the world’s largest lake.

Lagoon

Aerial view of swimmers in the Blue Lagoon geothermal spa, Iceland
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Lagoons are similar to seas in that they’re connected to the ocean, similar to lakes because of their surface area, and similar to ponds because of their depth. The official definition of a lagoon is a shallow body of water separated from larger bodies of water by a natural barrier such as a sandbar or coral reef. They can be considered "leaky" if there’s an uninhibited flow of water between the ocean and the lagoon, or "choked" if the connection is hindered by a narrow channel. Lagoons receive most of their water from the ocean instead of from rivers or springs.

Ocean

Clear, blue waters of the Pacific Ocean
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Lastly, we have Earth's mighty oceans. Oceans are the largest and deepest bodies of water on the planet. They make up about 70 percent of the Earth’s surface area and can reach depths of more than 36,000 feet. Oceans are easy to differentiate because there are only five of them — Pacific, Atlantic, Indian, Arctic, and Southern — and they’re so massive that it’s hard to mistake them for anything else.

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