by Elaine Robbins

About the author: Elaine Robbins is a writer for E Magazine, an environmental issues publication.

An inevitable part of many 1950s science documentaries was an awestruck tribute to our ability to “tame nature”—by building huge dams and controlling the flow of mighty rivers. There are an estimated 800,000 dams on the planet and 40,000 large dams—an incredible 20,000 in China alone.

The really big dams are the largest structures ever built by man, engineering marvels as awe-inspiring as the great pyramids of Egypt. And they rival the pyramids for the sheer magnitude of construction: It took 5,000 workers on 24hour shifts for five years to build the colossal Hoover Dam.

A growing coalition is trying to remove the Glen Canyon Dam in Arizona and restore the Colorado River’s original flow...