Today’s Wonder of the Day was inspired by Jeff. Jeff Wonders, “What is a lagoon” Thanks for WONDERing with us, Jeff!

Have you ever been stranded on a deserted tropical island? Probably not! But if you ever are, we hope it has a lagoon!

If you've ever seen a movie or TV show that takes place in a tropical paradise, you may have seen people swimming in a shallow pool of water that's split from the larger ocean by coral reefs or small  islands. That's a lagoon!

Of course, lagoons aren't just in tropical areas. They're common features along coastlines all over the world. Where there's a shallow body of water separated from a larger body of water by a reef or an island, you've got yourself a lagoon. In fact, the word “lagoon" comes from the Italian laguna, which describes the waters around Venice.

Although some people include bodies of fresh water as lagoons, others only apply the term “lagoon" to bodies of salt water. If a body of water that might be a lagoon receives an inflow of fresh water, it most likely will be called an estuary.

Just because a body of water fits the definition of lagoon doesn't mean it'll have “lagoon" in its name. Pamlico Sound in North Carolina, Great South Bay in New York, Banana River in Florida and Lake Illawarra in New South Wales are all technically lagoons despite their names.

Lagoons tend to form along coastlines with a gentle slope. This makes most lagoons shallow and sensitive to changes in sea level. If the sea level drops, the lagoon may dry up. If the sea level rises, the reefs or islands may end up below water.

Some of the most breath-taking lagoons are in tropical areas near coral reefs. When these lagoons happen to be pretty deep and are surrounded by ring-shaped coral reefs, scientists call them atolls.

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