Which environmental issue is commonly associated with hydroelectric dams?

• A. Increased greenhouse gas emissions from dam operations
• B. Nutrient buildup in water
• C. Air pollution from fossil fuel combustion
• D. Deforestation due to mining

Answer: (B)

Damming a river changes how nutrients and sediments move, so nutrients tend to accumulate in the reservoir. The slower, still water behind the dam lets sediments settle and nutrients like nitrogen and phosphorus build up, which can fuel algal blooms and degrade water quality inside the reservoir. This buildup behind the dam is a common environmental consequence of hydroelectric projects.

The other options don’t fit as directly. Greenhouse gas emissions from dam operations aren’t the most characteristic issue—though some reservoirs can emit methane, it’s not the defining problem. Air pollution from fossil fuels isn’t caused by the dam itself, since hydroelectric power reduces that pollution. Deforestation due to mining isn’t a direct outcome of creating a dam.