Fishing was prohibited in that lake, and Martins had a job to do. He put on the tee shirt that identified him as an "environmental agent" and hurried down the steps of his stilt-legged house. He pushed an aluminum skiff off the muddy river bank, and with a pull of the starter rope, the motor sputtered to life.

It surely was not a pleasant prospect: one lone, unarmed man confronting four poachers on an Amazonian night. But Martins was a man of authority, a tough veteran of this watery frontier and president of his community association. Moreover, the rules he was about to enforce had the full support of the community and the backing of Brazilian law.

Martins drew his skiff up alongside of the strangers' boat and asked them if they knew they were fishing illegally. "They said yes, they knew," Martins recalled. "I asked them to leave, and they did. Thankfully, most of the time it's like this."

Instead of a corps of professional guards, volunteers like Martins enforce the regulations in the Mamirauá reserve.

They learn part of what they need to know from a 3-5-day course given by Brazil's environmental agency. The rest comes from their intimate knowledge of the reserve's people and its environment.

Rough and ready though it may be, enforcement in Mamirauá is far more effective than in many other protected areas in Latin America, where park administrators don't have money to hire more than a tiny fraction of the guards they need to patrol vast areas. Logging, hunting--even clearing the forest and establishing homesteads--are often carried out with impunity in such "paper parks."

Community decision-making and volunteer enforcement have already shown results in Mamirauá. Fish populations have come back, boosting local incomes. Nearly all the families have outboard motors, freeing them from depending on middlemen fish merchants.