"He kept saying, 'This will be gone, all this will disappear,'" Orrego recalls. He spent three months researching plans for the proposed multimillion-dollar project and discovered it would separate 101 indigenous Pehuenche Indian families from their ancestral lands and flood 34 sq km of richly diverse forest, dooming 14 plant and animal species to extinction. In short order Orrego's Action Group for the Bio-Bio was born.

Orrego, 47, already knew something about resistance. He fled Chile temporarily in 1974 after the rise of General Augusto Pinochet Ugarte's military regime, moving to Toronto to study environmental sciences and later working with Mexico's Huichol Indians. And Orrego had earlier witnessed the anti-Vietnam War movement up close, as a teenager transplanted in the 1960s to New York City, where his parents were teaching. In those days he watched and learned. This time the fight was his.

Orrego's group has waged an uphill battle. Despite organizing protests and bringing a lawsuit, Orrego failed to stop construction of the Pangue, a smaller dam on the Bio-Bio. And plans for a second dam, the Ralco, have stirred mixed feelings even among the Pehuenche Indians. While some of them have joined in demanding a legal injunction against the dam because it would flood ancient burial grounds, others covet the payments they would receive if the project proceeds. Only the international conservation community is united behind Orrego; he won a Goldman Environmental Prize this year.

Such support spurs him to carry on from an austere office in Santiago, where he often sleeps on a futon. He sees the dam as a short-sighted scheme that spells tragedy not just for his five children but for all the children to come. "This place could keep giving water, giving biodiversity--for centuries," says Orrego, "and we are on the point of destroying it."

Reported by Elizabeth Love /Santiago