The Great Barrier Reef is the largest living structure on Earth and is visible from space.

The Great Barrier Reef sits in the Coral Sea off the coast of Australia. It covers 344,400 square kilometers. This area is larger than the United Kingdom and Switzerland combined. The reef is not one single piece. It consists of nearly 3,000 individual reefs and 900 islands.Tiny organisms called coral polyps build the reef. They take calcium carbonate from the ocean water to create hard shells. When polyps die, their skeletons stay behind. New polyps grow on top of the old skeletons. This process has happened for thousands of years to create the structures seen today.The reef supports a huge variety of life. It is home to 1,500 species of fish and 30 types of whales and dolphins. It also contains 411 types of hard coral. The reef acts as a natural barrier. It protects the coastline from strong waves and erosion.Corals are sensitive to heat. If the water stays too warm, corals lose the colorful algae that live inside them. This makes the coral turn white. Scientists call this coral bleaching. The Australian Institute of Marine Science tracks these events to help protect the reef.