Foil balloons are pretty. They’re shiny. And they last a long time. But what happens if the metallic balloons get loose? Turns out, they cause big problems. The people of New Orleans, Louisiana, learned this the hard way.

Last Tuesday, a wayward balloon hit power lines. Those lines were near a New Orleans water treatment plant. The power went out for just a moment. But that was enough to knock out four important water pumps. 

Workers weren’t able to get the pumps restarted for a while. The water pressure in the city’s system dropped. Low pressure can allow bacteria to enter through leaks. That could make people sick. So officials told residents to boil their water for a few days. (Boiling water kills germs.) 

Utility companies have warned about foil (or Mylar) balloons for years. What’s the problem? These balloons are made from thin plastic with a metallic coating. The coating conducts electricity. When the balloons hit power lines, they can create short circuits. That means the electricity doesn’t go where it is supposed to. The party decorations can even spark electrical fires. 

One electric company reports there were 582 balloon-related outages in the United States last year. 

Here are a few safety tips:

• Keep foil balloons indoors.
• Tie balloons to weights. Or attach them to furniture.
• Deflate them when your celebration is over. Put them in the garbage can—not outside.

There’s another problem with free-floating balloons. They turn into litter. Birds, turtles, and other animals sometimes try to eat the pieces. That can hurt or kill them. 

Whew. That’s a lot of good reasons to keep balloons where they belong.