Below normal water temperatures cause "cold water shock" when someone falls overboard or a boat capsizes in an icy lake or river. Cold water shock causes an involuntary gasp as the victim's head is plunged underwater, so the victim inhales water instead of air. Unless the person is wearing a life vest, drowning is a probable outcome.

“The shock of a fall into cold water is certainly one of the biggest hazards for early season anglers,” said Tim Smalley, DNR boating safety specialist. “The gasp caused by sudden immersion in icy water can cause the victim to inhale water and drown if they aren’t wearing a life vest.”

It was once thought that good swimmers who drowned after falling overboard into cold water were succumbing to heart attacks, Smalley said. While that may have happened to some victims, researchers find that most drown due to the torso reflex rather than a cardiac episode.

“The torso reflex is the gasp that happens when your face and chest suddenly enters cold water,” Smalley said. “The gasp is automatic and nearly impossible to stop. If your face is underwater when it happens, it’s often fatal, unless of course you’re wearing a life vest.”

Boats must have one U.S. Coast Guard approved wearable personal flotation device (life jacket) of the proper size for each person readily accessible on board. Boats 16 feet and longer also must carry a U.S. Coast Guard approved type IV throwable seat cushion or ring buoy on board.

The DNR recommends that everyone wear life jackets. “While the emphasis tends to be on children wearing life jackets, it’s the adults who die most often in boating accidents,” Smalley said. “There have been a fair number of cases in Minnesota where an adult has drowned in a boat accident, but the child who was wearing a life jacket was just fine.”

- Timothy M. Smalley, Minnesota DNR boating education program administrator