Australia's Great Barrier Reef is home to one of the world's largest networks of marine protected areas. Like other marine reserves, large segments of the Great Barrier Reef have strict rules against human activities, such as fishing and polluting. New research shows that protected areas can help stop the decline of aquatic life-including fish and corals-and sometimes even increase their numbers. The evidence suggests that designating protected regions is an effective way to improve the outlook for marine life in the increasingly threatened ocean.