“No one burns anything if they’re satisfied,” said Altair Donizete de Oliveira, a union leader here in Brazil’s western frontier. He listed salaries, cramped living quarters and requests for more home visits among the grievances that were contributing to the festering tension among the laborers, who number in the tens of thousands at various work sites in the Amazon.

Image Credit... The New York Times

Brazil is leading a rush among South American nations to build an array of dozens of dams in the Amazon. The authorities expect at least 20 important hydroelectric projects, including the Jirau and Santo Antônio Dams here in Rondônia State, to be built in Brazil over the next decade. Elsewhere in the Amazon, work has begun on Brazil’s biggest dam project, Belo Monte, an effort to divert the Xingu River requiring more than $12 billion.

The advance of the projects has opened Brazil to criticism from environmental groups, which say that the displacement of indigenous peoples and the flooding of swathes of rain forest — potentially releasing large amounts of methane gas — outweigh the dams’ benefits.

But officials argue that Brazil needs the dams to meet the demand for electricity, which is predicted to surge 56 percent by 2021. President Dilma Rousseff forcefully defended the projects in April, accusing opponents of living in a “fantasy” realm if they thought Brazil could improve living standards with renewable energy alone.

“I have to explain to people how they’re going to eat, how they’re going to have access to water, how they’re going to have access to energy,” Ms. Rousseff said.