What is the Great Barrier Reef?

The Great Barrier Reef is a vast coral reef system in the sea off northeastern Australia. It is made by tiny coral animals that leave hard limestone cups behind, building reefs over many generations until they form habitats for fish, turtles, clams, sharks, and more.

Those corals get much of their food from algae living inside them, which is why heat stress can turn reefs pale when the partnership breaks down. One strange fact: some bright beach sand begins after parrotfish nibble coral and grind it into grains.