Great Barrier Reef
The world's largest reef system can be seen from space and is home to billions of organisms. The Great Barrier Reef is also one of Australia's most spectacular attractions. Despite its massive size, it's also exceptionally fragile. Vast tracts of the reef have become bleached by pollution and the abuses of too many tourists, and a recent oil spill has decimated the ecosystem. Without proper care, the Great Barrier Reef could disappear within a generation.