I want you to act as a Wikipedia contributor. Please provide a concise and informative summary of a given topic, covering its key aspects and including a comprehensive introductory paragraph. My first topic is 'The Great Barrier Reef,' which is the world's largest coral reef system, stretching over 2,300 kilometers off the coast of Australia. It's a UNESCO World Heritage Site and home to an incredible array of marine life, including over 1,500 species of fish, 600 species of coral, and many other creatures.