Already Latin America's biggest economy, Brazil envisions a future requiring massive amounts of electrical power for its expanding industries and growing cities.

The response has been a construction boom that will install — and that's generating plenty of controversy, particularly from environmentalists.

In the jungles of far-western Brazil, workers drill and hammer on one end of the giant Jirau hydroelectric dam. It's a massive complex that, when completed, will stretch five miles across the Madeira River.

It takes several minutes to drive over an earthen berm to reach the power houses, where workers prepare to install giant turbines.

Everything about this dam in Rondonia state is on a supersized scale. It will hold enough concrete to build 47 towers the size of the Empire State Building, according to Jose Gomes, a civil engineer who's the institutional director for the Jirau dam.

This will be the third-largest dam in Brazil, Gomes says, and the 14th biggest in the world. He adds that no other dam will have as many turbines — 50 of them, each big enough to accommodate a locomotive.

All of this, from the huge steel reinforcements to the spillways, are to produce electricity for Brazil's largest city, Sao Paulo. That's more than 1,400 miles away from the power source — the mighty Madeira, the largest tributary of the Amazon.

Many Projects In The Works

But this dam is just one of many that will be built over the next decade. The environmental group International Rivers, which tracks Brazil's dam-building plans, says 168 will go up in the Amazon alone.

Many will be small, to regulate water flow or to power a single industrial project. The Energy Ministry lists 34 sizable dams by 2021. The goal is to harness some of the world's greatest rivers.

Paulo Domingues, director of energy planning for the Energy Ministry, says that will permit Brazil to increase its electrical generation capacity by 50 percent.

"Only hydroelectric dams can keep up with the annual increase in demand for electricity," says Domingues. The costs of running thermal-electric, gas or oil-fired plants is too high, he says.

But hydropower in the world's biggest and most biodiverse forest has fueled criticism. The Amazon absorbs much of the world's carbon emissions, regulates the climate and produces a fifth of the world's freshwater.

And its rivers are key in all of that. Indians across the Amazon say the dams will unalterably change their way of life.

Uprooting People

Christian Poirier, who works with the group Amazon Watch, says the government has swept aside such criticism while seeking economic growth at all costs.

"It's done so in a way that ignores human rights, ignores the letter of the law, ignores its own legislation and international conventions," Poirier says.

Here at Jirau, those affected by the dam are fishermen and hunters. They'd lived a simple life on the Madeira River — then the dam started to go up.

More On Brazil

Jeferson Campos says now there's no more fishing, no hunting, no gathering of wild fruits. Now, his family's home is under water.

Jose Gomes, the institutional director of the Jirau dam project, counters that families like Campos' were given new homes in a new town, Nova Mutu. With 1,600 new houses, the town was built from scratch by the consortium that's installing the Jirau dam.

He also says the dam has fish ladders so fish can migrate upstream, and that the flooding created by the dam has been relatively small by the standards of the dams of the past.

Construction is now proceeding rapidly, with 18,000 workers toiling to get the dam online by 2015. On a recent day, as some workers put up steel reinforcements, others worked to unhinge a cable that had become stuck in a spillway filled with water. Divers were sent down; they kept in touch with radio operators on the surface.

Gomes watched it all closely and remarked on the larger goal.

"For Brazil to keep up with demand, two giant dams, just like this one, must go up every year," he said.