Brazil: Harnessing the Parana

Brazil's many and mighty rivers offer a wealth of power-producing capacity, but less than 10% of the country's hydroelectric potential is utilized. Even major cities suffer from a severe kilowatt lag. In Rio de Janeiro, lights often flicker—and sometimes die—and Säo Paulo's massive industrial complexes are perennially pestered by a shortage of juice. Prospects are brighter: a giant project abuilding in south-central Brazil will help illuminate some of the country's dark corners and produce a stream of electricity for its cities.

The Paraná, third biggest river in South America after the Amazon and the Orinoco, is being harnessed by two...