Brazil is building a major hydroelectric dam on the Amazon River -- the first such project since the 1980s, when a series of huge new reservoirs triggered environmental disasters across the region. This time around, however, Brazil's engineers are determined not to make the same mistakes: The new dam will include features such as a "fish ladder" to allow aquatic life to circumvent the dam, and a low-pressure turbine to reduce the amount of land that needs to be flooded. If the dam is a success, Brazil plans to spend $100 billion building as many as two dozen hydro projects in the next decade.

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