Pontoon Rafting, Grand Canyon National Park, Arizona, 2006Photograph by Michael NicholsRafters aboard a motorized pontoon boat get a thorough soaking on the rain-swollen Colorado River in Arizona's Grand Canyon National Park. Each year, some 22,000 visitors board rubber paddle rafts, oar-powered wooden dories, and luxury motorized rafts to ply this storied stretch of the Colorado's waters.