The Everglades are swampy grasslands that cover southern Florida.
Everglades National Park, which covers only a fifth of the Everglades region, was established to preserve this unusual ecosystem, for example, it is the only place in the world where alligators and crocodiles live together.
The park covers 2,342 square miles (6,090 sq km). It is also a World Heritage Site, an International Biosphere Reserve, and a Wetland of International Importance.
The Everglades are in danger today for several reasons, primarily because their water supply has been threatened.
The region depends on rainfall, but human activities in the surrounding areas siphon off much of the water before it can reach the park. Pollutants are also entering the area, causing damage to vegetation and disruption to the food chain.
Mercury poisoning has killed at least one of the endangered Florida panthers there, a tragedy because there are probably fewer than 30 panthers left in the state.
The Everglades are now thought of as swamps, but a hundred years ago this watery area was a river 50 miles (81 km) wide and only 6 inches (15 cm) deep.
It flowed from Lake Okeechobee to the Florida Bay.
As people moved into this part of southern Florida, engineers interrupted the flow of the river by adding dikes, canals, and pipes to provide water to farms and homes.