July 10, 2011, 9:00 a.m., and the heat makes me wonder how people can live in South Florida in high summer. Paul Gray and I push our earmuff bands forward to hold down our hats and feel the welcome rush of cooling air as Don Fox guns his airboat out onto the heart, lungs, and kidneys of the Everglades—Lake Okeechobee. To our south, hidden by 467,200 acres of dry lake bottom and shallow water draped over the curve of the earth, lie Florida’s ever-thirsty sugarcane plantations, Big Cypress National Preserve, Everglades National Park, and Florida Bay. To our north the lake collects the now-feeble flow of its major artery, the damaged but recovering Kissimmee River. All this is part of the “greater Everglades.” Earth has no other place like this 4.5-million-acre grassland-and-savanna landscape, with its rich mix of salt, brackish, and freshwater habitats. The greater Everglades sustains species or subspecies of at least 1,030 plants, 60 reptiles, 75 mammals, 430 fish, 345...