by Joel Achenbach

About the author: Joel Achenbach is a staff writer for the Washington Post newspaper.

Cruising westward at 300 feet, the helicopter is heading straight for the end of civilization. You can see it just ahead. It’s a line across the surface of the Earth—a levee, built years ago to hold back the swamp. Now it works in reverse, restraining the developers. Beyond the levee there are no shopping malls, no houses, no roads, just a wet prairie full of alligators, lily pads and saw grass.

And there’s something new, something growing, spreading—a pale-green substance that seems to be crawling all over the tree islands that speckle this portion of the Everglades. The pilot takes the chopper down for a closer look. You can...