In October 1916, dignitaries gathered at the Rio Grande, near present-day Truth or Consequences, New Mexico, for an event said to be “of world-wide importance in the irrigation field.” It was the dedication of Elephant Butte Dam, then the largest impoundment reservoir in the world.

It would store the river's spring floodwaters. By regulating flows, it promised to “make the desert bloom” from Southern New Mexico to El Paso and Juarez.

But the dam also triggered a chain of unintended consequences. The riverside habitat was transformed. A century later, scientists are still tracking these sweeping changes.

The Chihuahuan Desert is outstanding in many respects. For example, ...