Be sure to wait at least 15 minutes after shutting off the motor before swimming off a boat. Anyone on water skis or an inner tube should ride at least 20 feet behind, too.

This summer there is a silent killer on the water that health officials want boaters to keep in mind. Carbon monoxide poisoning from boat motors has killed more than a dozen Minnesotans in the last few years.

Doctors believe that number is actually much higher, since people don’t seem to know much about the danger.

Minnesotans love their lakes. But, something that can’t even be seen can quickly turn a weekend treat into tragedy.

“The carbon monoxide off the back of a motor of a boat is equal to 166 cars,” said Kari Pearce with Trauma and Critical Care at the Hennepin County Medical Center.

It’s best to wait at least 15 minutes after turning the motor off before jumping into the water to swim off a boat. That’s how long it takes for the carbon monoxide to disperse.

Swim platforms usually found on houseboats can also be a big problem. They shouldn’t be used unless the motor is off.

Health experts say it’s hard to recognize what’s wrong if someone is overcome with carbon monoxide since people may think their symptoms are from being out in the sun all day.

“You might be feeling a headache, dizziness, might have a little nausea. You feel like the boat is rocking a little bit too much and you feel like that’s what’s causing it,” explained Pearce.

A boat shouldn’t drag anybody on skis or an inner tube closer than 20 feet, either. Any closer and carbon monoxide exhaust can kill.

“Just to be aware that it’s there because you can’t see it, taste it or smell it,” advised Pearce.