Everyone loves a good dunk in a scenic alpine lake. What could be more refreshing or more memorable? Besides being plain old fun, swimming helps freshen up your hiker funk and keeps you from overheating on hot days.
That said, you do need to be cautious about charging into frigid tarns and rivers without acclimating to the temperature. Everything is that much colder in the high country, and the water—often fed directly by melting snowfields and glaciers—is certainly no exception. Plunging into icy water can be bracing, but it may also be dangerous. Jumping into cold lakes and rivers without taking time to adjust to the temperature can send your body into shock and ultimately drown you.
According to the National Weather Service, the sheer shock of sudden immersion in cold water can trigger an involuntary gasping response and hyperventilation. If your head goes under water, you’re at risk of inhaling a lot of cold water into your lungs at this point. In addition, hyperventilation and shock cause your heart rate and blood pressure to spike. In vulnerable people, this could trigger a stroke or heart attack.
If you stay in cold water long enough (generally more than five to 15 minutes), your blood vessels will constrict, limiting blood flow to your extremities to conserve heat. This can lead to a condition known as “cold water incapacitation,” which is exactly what it sounds like. You lose control of your muscles and nerves, preventing you from swimming or treading water.
Interestingly, all of the above indicates that hypothermia is actually not the biggest threat to a backpacker who suddenly becomes immersed in cold water. Hypothermia primarily affects people who have a life jacket to keep their heads above water long enough for the condition to become life-threatening (typically 30 minutes or longer, but it depends on water temperature). For a backpacker who almost certainly doesn’t have any flotation device, the gasp response and cold water incapacitation are far more immediate threats.
That being said, if you get out of cold water and the air temperature drops (a thing that can happen easily in the mountains), you’ll still be at risk of hypothermia at that point. Change into warm, dry clothes and get into your sleeping bag if necessary.
How to Avoid Cold Water Shock
But all this doesn’t mean you can’t swim at all—you just have to ease in gradually. You can swim in cold water safely if you allow your body to acclimate to the temperature rather than shock it with sudden immersion. Test the water before jumping in, and gradually immerse yourself for a few minutes before doing a cannonball.
Don’t let the air temperature lull you into a false sense of security. Remember that mountain water is often shockingly cold, even on hot summer afternoons.
For maximum safety and maximum fun, don’t just tread water. Set sail on USS Inflatable Sleeping Pad, the makeshift flotation device most backpackers already carry. Your inflatable pad can help keep you afloat if you start to lose muscle control. Also, it will help keep your whole body near the sun-warmed surface of mountain lakes.
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The water doesn’t even have to be particularly chilly to put you at risk of cold water shock. Water as warm as 70 degrees Fahrenheit can still induce the gasp response. Even if you don’t experience hyperventilation or an elevated heart rate, if you find yourself shivering in the water, it’s too cold, and you should get out.
If you do become suddenly immersed in cold water—intentionally or not—the best thing you can do is stay calm. Focus on keeping as much of your body out of the water as possible, especially your head and chest, and get out as quickly as possible.
Dying from cold water shock is rare. However, hikers sampling frigid alpine streams and lakes are more at risk than the general population.
To be clear, I’m not trying to ruin your fun. I love a good alpine swim as much as the next hiker. If you want to swim in that gorgeous tarn below the trail, you absolutely should.
Just make sure you ease yourself in gently. The whole “rip the bandaid off” mentality may not serve you well in this scenario. Sure, plunging in without acclimating could put a few metaphorical hairs on your chest. But it could literally cause your chest to seize up and kill you, too, which hardly seems worth it. Let your body adjust to swimming in a giant puddle of glacial meltwater first, and you’ll have a grand time.
Featured image: Berg Lake in Mt. Robson Provincial Park, Alberta, Canada.
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