A dam blocks a stream or river. This blockage forms a reservoir. That’s a word for a manmade lake. The first dam that we know of was built in Egypt around 3000 BCE.
Many dams were built in the last century. More than 45,000 major dams have been built in 150 countries. Six out of every ten rivers in the world has been dammed. These changes have actually changed the way Earth wobbles as it spins.
Dams do many great things. They reduce flooding. They also help make electricity and get water to farms. Dams supply drinking water for millions of people.
In recent years, it has become clear that dams also do bad things. Some artificial lakes flood homes. That forces many people to move. They also destroy forests, farmland, and many native species. Building dams also creates pollution.
