[MUSIC] Joan Cartan-Hansen, Host: Dams are amazing to see, but if you are going to visit, you do need to be careful.

Be sure to obey all posted signs and, if you're recreating, stay well away from the dam itself.

While dams are engineering marvels, every once in a while, they do fail.

On average, ten dams fail in the U.S.

every year.

Most of these are very small, causing little damage.

But when a major dam fails, it can be catastrophic.

The most famous failure in Idaho happened in 1976.

Engineers had just built the Teton dam when it collapsed.

>>"People downstream better get out."

The residents of Wilford had only a few minutes of warning before 80 million gallons of water ripped through their homes.

Flood waters wiped out many communities And destroyed thousands of acres of farm land.

In the end, the flood cost American taxpayers almost half a billion dollars.

Engineers learned a lot from the Teton dam failure.

They're using that new knowledge to make today's dams safer.

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

You'll find it at science trek dot org