Dams

A dam is a big wall built across a river to block the flow of water. The water collects behind the dam and forms a lake called a reservoir. People use dams to store drinking water, prevent floods, and make electricity. Dams are some of the biggest structures humans have ever built.

How Dams Make Electricity

Water stored behind a dam has a lot of energy. When the water flows through pipes in the dam, it spins giant wheels called turbines. The spinning turbines power machines that create electricity. This is called hydroelectric power, and it does not cause air pollution.

Types of Dams

Some dams are made of concrete and shaped like an arch. Others are made of packed earth and rocks. Arch dams are curved so the water pressure pushes against the canyon walls. Earth dams are wider and can be built in flat areas where there are no canyon walls to lean on.

Fun Facts

• Beavers are nature's dam builders. They use sticks and mud to build dams in streams.
• The Three Gorges Dam in China is the world's largest power station. It can make enough electricity for millions of homes.
• Some dams are so big that the lakes behind them can be seen from space.

Did You Know?

The oldest known dam was built about 5,000 years ago in Jordan. It was made of stone and earth to store water in the desert.