Swimming and Hypothermia

Here’s a bit of information on hypothermia we’ve compiled for my swims over the past few years. Because the water in Juan de Fuca Strait is so cold I have asked my crew become familiar with it.


Hypothermia is a state of prolonged low body temperature that is broken into 3 stages: mild, moderate, and severe. Swimmers begin the long, slow decline in body temperature as soon as they enter the water. Hypothermia is inevitable in long open water events, but the severity of hypothermia depends on how well the swimmers are able to maintain their body temperatures.

Someone with hypothermia usually isn’t aware of their condition, as it often begins gradually. Added to that, confused thinking associated with hypothermia can cloud self-awareness, which can lead to risk-taking behaviours. Routine monitoring of swimmers for signs and stages of hypothermia is a critical task for support crew.

Signs and symptoms of hypothermia will present differently with swimmers than what is typically seen on land. Here is a list of signs and symptoms to watch for and document. If concerned or in doubt, crew must report their findings up to the escort boat.

Signs of mild hypothermia include:

  • Decreased coordination/dexterity, especially fingers
  • Slight confusion, mental fog
  • Fatigue, slight decrease in stroke rate
  • Shivering
  • Dizziness
  • Hunger
  • Nausea
  • Faster breathing
  • Trouble speaking, slurred words
  • Increased heart rate
  • Skin may appear pale on hands and feet
  • Slight decrease in stroke rate

As your body temperature drops, signs and symptoms of moderate to severe hypothermia include:

  • Shivering, although as hypothermia worsens, shivering stops
  • Increased clumsiness or lack of coordination
  • Slurred speech or mumbling
  • Grumpy
  • Confusion and poor decision-making, difficulty answering simple questions
  • Drowsiness or very low energy
  • Lack of concern about one’s condition
  • Pale skin gradually moving up the arms and legs
  • Blue lips
  • Noticeable decrease in stroke rate

Swimmers should be removed from the water if they have moderate or severe hypothermia.  There is a sever danger of drowning in this late stage. Signs include:

  • Progressive loss of consciousness
  • Weak pulse, irregular heart rate
  • Slow, shallow breathing

Diagnosing hypothermia in swimmers

  1. Check stroke count per minute every half an hour. If the stroke rate changes dramatically over the course of the swim the swimmer may be suffering the effects of hypothermia
  2. Watch the swimmers body position. If they are hypothermic, they may lose the ability and energy to co-ordinate kicking, and may slip into a more vertical position in the water (their feet will sink). This may also appear as a dramatic decrease in performance and forward progress.
  3. Simple questions become complex when someone is hypothermic. Ask them some moderately complex question (days of the week in reverse, counting backward, math or trivia questions).
  4. Watch how they handle feed bottles. Are they able to open a simple bottle cap or peel a banana? Dexterity is impacted by hypothermia.
  5. A swimmer who is experiencing violent shivering should be immediately removed from the water.


Helping the swimmer cope with hypothermia

  1. Add fuel through food.

Low blood sugar and low caloric intake will significantly affect a swimmer’s ability to maintain body temp, athletic performance, and mental alertness. A low blood sugar level will worsen signs of hypothermia, and will contribute to low mood, muscle cramping, and fatigue.

Your swimmer cannot wait until they are hungry to eat, they must stay a step ahead of their caloric needs. Encourage them to eat on a regular basis, even if they disagree.

  1. Manage beak time.

The longer the exposure to water, the greater the risk of hypothermia. The swimmers will be in the water for up to 50 hours. If the swimmer breaks every 30 minutes for 5 minutes that is just over 8 hours of break time. If breaks are limited to 3 minutes the swim will be 3 hours less.

Shorter breaks throughout the swim will mean less time overall in the water. Keep in mind this is a risk vs benefit as swimmers will need social interaction and physical rest throughout the swim.

Movement generates heat. Shorter breaks also mean less time not moving.

3 thoughts on “Swimming and Hypothermia

  1. Susan,
    Thanks for sharing the details. It is incredibly interesting and makes me appreciate even more your amazing adventures.
    Looking forward to tracking your progress and hoping being there when you reach Victoria.

  2. Thank you for this Susan. I believe that one of the first signs of hypothermia is the onset of Claw Hand. The two fingers furthest away from the thumb on both hands become unresponsive and curled-in as a result of the cold, and this effects the speed of forward motion as the hand no longer remains fully cupped.
    Time to get out of the water!
    All the Best

    1. Hi John. Yes, I had heard that as well. I have never experienced it myself. Hypothermia is definitely a challenge when we are in the water as the symptoms seem to be so different for everyone. One of my challenges is the amount of time it takes me to shiver, which is where I personally draw the line. I have heard that others though, swim through it.


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