A small bucket loader scraped Wahweap Bay’s expanding strip of red mud and gravel, its operator smoothing the shoreline where concrete workers were busy chasing a lake in retreat.

To the left, where the bay had long offered kayakers and water skiers a loop around Lone Rock, the monumental slab now rose from dust flats instead of from flat water. To the right, in the channel that leads to Glen Canyon Dam and the Colorado River’s sunken bed, formerly submerged islands and peninsulas mapped out a warming climate’s continuing transformation of one of America’s great water stores and pleasure grounds.

A desert flooded by impounded waters in the last century has visibly reasserted itself in this one.