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Building dams may alter the ecosystem of the river or stream by blocking fish migration routes and negatively impacting other wildlife. It may also cause adverse effects on cities downstream that rely on the river for drinking water and food.

There are several advantages to building dams. Our demand for water has been increasing. Dams store water and supply it when needed. They can sometimes stop a river from overflowing and prevent floods. Dams also protect clean water and can generate electricity with less pollution than other methods.