Most people gasp as soon as they sink into freezing water — and then that same water rushes in to fill their lungs.

“Unless you’re trained to fight it — when your head goes under, it’s a reflex,” said Const. Marshall Bushell of Hamilton police.

“Chances are, you’re going to go unconscious. Then it’s all downhill from there.”

On Tuesday morning, the police marine unit held a mock rescue on the ice by Pier 4 to show just what goes into a cold-water rescue. Media officer Const. Debbie McGreal-Dinning volunteered to take the plunge — albeit in a marshmallow man-esque dry suit.

mcgreal dinning ice safety

McGreal-Dinning said the cold water was surprisingly "refreshing." (Adam Carter/CBC)

The water itself was (mercifully) warmer than it has been all winter, at just a couple of degrees below freezing. McGreal-Dinning donned her suit, marched out onto the ice, and started jumping up and down to break through.

After a couple of attempts, a crack echoed over the bay and she sank under. “As soon as you feel that cold water on your face, the automatic reaction is to inhale. It would be pretty scary,” she said. “The water is a real shock to the system.”

That’s why police are tying to get a simple message out: “no ice is safe ice,” Bushell said.

“A lot of people don’t realize that all it takes is a little moving water to make it unsafe,” he said. “Or if there’s snow cover — you can take one wrong step and the next thing you know, you’re in the water.”

The police marine unit is usually called to a couple of cold water rescues a year — though this year, incidents are down because the ice is so dense. In some places in the harbour, the ice has frozen a metre thick, Bushell says.

In fact, the Great Lakes ice over reached 91 per cent this winter — the second highest ever seen on record. It was 93.9 per cent back in 1979.

But even with those record numbers in mind, people should still be careful marching out onto any water source, Bushell says. “We’re not going to go out there and say ‘that is safe.’”