Today, on a remote stretch of the Elwha River in northwestern Washington state, a demolition crew hired by the National Park Service plans to detonate a battery of explosives within the remaining section of the Glines Canyon Dam. If all goes well, the blasts will destroy the last 30 feet of the 210-foot-high dam and will signal the culmination of the largest dam-removal project in the world.

In Asia, Africa, and South America, large hydroelectric dams are still being built, as they once were in the United States, to power economic development, with the added argument now that the electricity they provide is free of greenhouse gas emissions. But while the U.S. still benefits from the large dams it built