ocr: The Grand Managed Canyon Target of five million tourists a year, Grand Can- yon National Parki is also invaded by frequent air pollution as on a May morning (following pages). Restrictions to reduce noise from sight- seeing airplanes and helicopters are being phased in. On the Colorado River, boaters encounter an ecosystem transformed by Glen Canyon Dam upriver. Still unresolved: Can all the canyon's competing interests be satisfied? By MICHAEL E. LONG Photographs by PETER ESSICK 117
