Like other dictators, Paraguay's Alfredo Stroessner staked his regime's claims to modernity on a massive hydroelectric project, Itaipú Dam. Critiques of dams tend to focus on environmental degradation caused by flooding, forced displacement of communities, and fiscal malfeasance. But Itaipú, the world's largest dam, also participated in the Stroessner regime's secret police terror apparatus. A series of formerly classified documents about Itaipú Dam show how the secret police used the dam in its security and intelligence apparatus to violently suppress any opposition. They also reveal how the opposition to the Stronato grew and mobilized around the dam. By interlacing these two threads, this historical ethnography explores “hydroelectric statecraft” in Itaipú Dam—that is, how the harnessing of the dam's resources has given rise to particular political practices and structures within Paraguay.