Lagoons are separated from larger bodies of water by sandbars, barrier reefs, coral reefs, or other natural barriers. The word “lagoon” derives from the Italian word laguna, which means “pond” or “lake.”
Although lagoons are well defined geographically, the word “lagoon” is sometimes used as a name for a larger region that contains one or more lagoons. For example, Laguna Madre on the Texas Gulf Coast is actually made up of smaller bays and lagoons, while Laguna Beach in Southern California is actually a beach and not a lagoon at all.
There are two types of lagoons: atoll and coastal. Atoll lagoons form when an island completely subsides beneath the water, leaving a ring of coral that continues to grow upwards. At the center of the ring is a body of water that is often deep. The combination of coral growth and water creates a lagoon. It may take as long as 300,000 years for an atoll formation to occur.