From Alligator Alley (I-75), the Everglades River of Grass covers as far as the eye can see. The water is only a few inches deep but as many as twenty miles wide without so much as one tree island. The muck bottom of such areas is so thick and impassable to humans that many places in the Everglades, which are crossed by air by millions of people, have most likely never felt the pressure of a single human footprint.