Once called the "valley of death" and the "most polluted place on earth," Cubatao, Brazil, is a symbol both of severe environmental degradation and how people can work together to clean up their environment.A determined effort to reduce pollution and restore the badly contaminated air and water in the past decade has had promising results. While not ideal by any means, Cubatao is no longer among the worst places in the world to live.

Cubatao is located in the state of São Paulo, near the Atlantic coastal city of Santos, just at the base of the high plateau on which São Paulo—Brazil's largest city—sprawls. Thirty years ago, Cubatao was an agreeable, well-situated town. Overlooking Santos Bay with forest-covered mountain slopes rising on three sides around it, Cubatao was well removed from the frantic hustle and bustle of São Paulo on...