NORTHWEST MONTANA — With stream fishing in Montana opening May 19, the third Saturday in May, Montana Fish, Wildlife and Parks reminds anglers that fish from boats that even on a warm day the water temperatures may be in the low 50s or cooler.

U.S. Coast Guard statistics show that in water below 60 degrees a boating accident is five times more likely to be fatal.

“Cold water can be fatal in ways that you might not expect,” said Liz Lodman, FWP boating education coordinator.

Lodman said most people are aware that cold water immersion can cause hypothermia - the abnormal lowering of the body’s core temperature.

“What so many people don’t realize is that cold water immersion has several stages — any one of which can be fatal,” she said.

Victims who experience an unexpected fall overboard suffer cold water shock in the first minute. The shock causes them to involuntarily take a series of big breaths, called hyperventilation. If their head is underwater, they can inhale more than a quart of water and drown immediately.

“People lucky enough to keep their head above water will continue hyperventilating, as their blood pressure jumps,” Lodman said.

“If they can’t control their breathing within 60 seconds, they will suffer numbness, muscle weakness or even fainting, which also quickly leads to drowning,” she said. “A person with heart disease may die on the spot due to cardiac arrest.”

Victims who survive the first minute of cold shock and hyperventilation quickly progress to “cold incapacitation” or swimming failure. With the rapid cooling of the extremities muscle stiffening occurs. A person is, within about 10 minutes, unable to swim, hold onto a floating object or put on a life jacket. Even yelling for help can be difficult.

Hypothermia is the third stage. Lodman said a common misperception is that hypothermia is immediate — but that is not the case. It may take 30 minutes to become hypothermic. Severe hypothermia can take an hour or more to set in, depending on the water temperature, body mass, clothing, the amount of struggling and several other factors.

Lodman said a body core temperature of 95 degrees is considered hypothermic, loss of consciousness occurs at about 86 degrees, and death is imminent when the core temperature drops below 82.

“Unless a person is wearing a life jacket, drowning will occur long before severe hypothermia sets in,” she said.

Most boating fatalities involve capsizing or falls overboard, not collisions between boats running at high speed.

“Too frequently a single boat on a lake capsizes, the victim isn’t wearing a life jacket, has no warning or time to put one on, and they drown due to the effects of cold water,” Lodman said.

Experts say ‘stay with the boat’ if you end up in the water. Even if you aren’t able to get back into the boat, you are more likely to be seen by rescuers.

“A person should not swim for shore unless they are wearing a life jacket, have no or very little likelihood of rescue, or they are close to shore and aren’t able to climb back into or on top of the boat,” Lodman said.

“A life jacket is the key to surviving an accident on the water,” Lodman said.

Lodman urges anglers to wear a life vest from the time they enter the boat until they return to shore.

“There is no time to put one on before a boating accident — accidents can rarely be predicted or foreseen,” she said. “It would be like trying to buckle your seat belt before a car crash.”

Montana’s first reported boat drowning of the season took place Easter Sunday on Medicine Lake in northeast Montana.