Atoll

An atoll is like a ring of sand and coral that surrounds a lagoon. Imagine that you are making a castle on the beach, but instead of just putting the sand in a pile, you make a big circle and build up the sand along the edges. Then, you add a bunch of pretty shells and colorful rocks all around the edge of the circle. The middle of the circle is where the water comes in and fills up the inside of the circle.

That's what an atoll is like, but on a much bigger scale. The ring of sand and coral can be hundreds of miles wide and the lagoon inside can be very deep. Sometimes, the coral in the sand can get so high that it sticks out of the water. These are called "islets" and they can be home to plants and animals like birds and lizards.

Atolls are usually found in warm, tropical places like the Pacific Ocean and are very important for the ocean's ecosystem. They provide a home for many different kinds of marine life like fish and sharks and are important for protecting the land from strong ocean waves. So, atolls are like huge, natural sandcastle circles that help animals and protect the land!