[MUSIC] Joan Cartan-Hansen, Host: More than seven percent of America's electricity comes from hydroelectric dams.

Dams create electricity using stored water.

Dams store water from rivers and spring melt into reservoirs.

Dam managers then allow water to flow through a long pipe called a penstock.

From the top of the dam to the bottom.

The falling water spins blades in turbines.

Those spinning blades are connected to a generator.

Those generators use magnets and copper coils to create electricity which is sent out on power lines.

Some rivers also have specially designed turbines to capture the power of moving water to create electricity.

But dams and turbines do change the course of rivers.

And that can be deadly for fish like salmon that need a free flow to migrate downstream.

Hydroelectric power is considered a green source of energy because it doesn't require the burning of fossil fuels.

Most dams in the United States don't generate electricity, but scientists say they could be a potential new source of power.

For more information about dams, check out the science trek website.

You'll find it at science trek dot org