Everglades

Unlike most of the early national parks in the United States, created for their scenic grandeur — mountains, canyons, geysers — the Everglades was declared in 1947 explicitly to protect an ecosystem for its biological value: a vast, very slow-moving river of grass draining towards Florida Bay. It is the only place in the world where the American alligator and the American crocodile occur together naturally. Decades of agricultural and water channelling across southern Florida cut its natural flow drastically, prompting from 2000 one of the largest wetland restoration projects in history, the Comprehensive Everglades Restoration Plan, at a cost of over 10 billion dollars.