Thirty-nine years ago, due to record-breaking snowfall in the Upper Colorado River Basin, Lake Powell rose substantially, catching river managers off-guard. By late June, the reservoir was nearly overflowing, forcing operators—for the first time ever—to rely on the spillways. Instead of giving relief, that precipitated a new crisis, as a phenomenon called cavitation sent shockwaves through the spillways’ innards, tearing through the concrete and then the sandstone, putting the colossal Glen Canyon Dam in peril. The spillways were repaired, and the dam survived. But now it is threatened yet again, only this time for the opposite reason. In March, Lake Powell’s surface level dropped to within 33 feet of the minimum needed to generate hydropower, for the first time since it was filled in the 1960s. If—or when—it hits that …
