Come summer's dog days and Americans tend toward extremes. Some exhaust themselves swimming, gardening or golfing while others conserve energy lolling about on back porches or public beaches. But a growing number of people, in the search for a happy medium, are rediscovering a sport as old as the first air-pressure auto tire-tubing.
Armed with sturdy inner tubes, floppy hats, buoyant coolers full of iced beer cans, and an extra car to leave downstream for the trip back, enthusiasts simply stake out a docile stretch of river, plop themselves into the tube's cool well, and float downstream. When...