The first known dam was built in Egypt around 3,000 BCE. Dams block the flow of streams and rivers to form a reservoir, or artificial lake.
In the last hundred years, dam building has exploded. More than 45,000 major dams have been built in 150 countries, altering 60 percent of the world’s rivers. This water redistribution actually causes a slight change in Earth’s wobble as it spins.
Dams provide great benefits. They prevent flooding, generate electricity, give farmers water to irrigate their land, and supply drinking water for millions of people.
In recent years though, it has become apparent that there are also many negative aspects to dam construction. Creating artificial lakes can force many people from their homes. Dams destroy forests and farmland, cause irrecoverable loss of native species, and create pollution.
