The guide, a river dweller of indigenous ancestry, slipped the outboard into neutral to keep his boat and cargo of six tourists from interrupting the tumult in the water ahead. There, scores of black caiman—the largest alligator in Latin America, measuring up to five meters (16 feet)—churned the surface of the lake, thrusting their long snouts underwater to snag fish emerging from a nearby stream.

Such scenes are a daily occurrence in this sprawling swath of seasonally flooded Amazon rainforest called the Mamirauá Sustainable Development Reserve. But the astonishingly rich wildlife here is just one attraction. No less striking is the conservation model that is preserving these resources and ensuring livelihoods for the reserve’s 7,000 people—a mix of Amazon Indians, descendents of rubber tappers and migrants from the nation’s northeast living in 78 riverside communities.

Created in 1996 in the western state of Amazonas, Mamirauá was the first of Brazil’s 26 sustainable-development reserves. In protected areas of that type, local communities may engage in economic activities that are found through scientific research to be consistent with environmental conservation.