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Cold water shock is a physiological response that occurs when a person is suddenly immersed in cold water. It is among the common causes of recreational boating deaths, and can occur even during the summer.
According to the Canadian Red Cross, from 1991-2000, boating accounted for 55% (51/92) of all cases of hypothermia without drowning, and 38% of all cold water immersion deaths (772/2,007).
Learning what to do to prevent and respond to cold water shock is vital for boating on Canadian waters, which remain cold throughout the year.
Key takeaways
- Cold water shock occurs when a person is immersed in water that is cold in comparison with their body temperature.
- Cold water shock can occur in relatively warm water.
- Canadian waterways are cold, making Canadian boaters at higher risk of cold water shock.
- Cold water shock can lead to drowning and death.
- The four phrases of cold water shock are: losing control over breathing; losing ability to move in the water; hypothermia and unconsciousness; cardiac arrest during or after rescue. However, symptoms vary in intensity and danger from person to person, with some people passing away from cardiac arrest or losing consciousness immediately.
- Once you are in the water, try to control your breathing, don’t panic, and call for help. Some people can swim to shore once their breathing has slowed. It’s important to get out of the water as quickly as possible in all cases.
- Boaters should do everything possible to avoid accidents like running aground or capsizing, and wear a PFD (life jacket) to minimize the risks associated with falling in the water.
Table of contents
- Cold Water Shock: Definition
- Symptoms of Cold Water Shock: Four Phases
- Stage One: Cold Water Shock (First 1 – 3 Minutes)
- Stage Two: Cold Incapacitation / Swim Failure (The Next 3 – 30 Minutes)
- Stage Three: Hypothermia (30 Minutes to Several Hours)
- Stage Four: Post-Rescue Collapse (During or After Rescue)
- The 1-10-1 Rule
- How to Survive Cold Shock
- 5 Tips to Avoid Cold Water Shock While Boating
- Frequently Asked Questions
Cold Water Shock: Definition
Cold water shock occurs when you are suddenly plunged into frigid waters. It can happen even in relatively mild water temperatures.
Cold water shock causes the body to react in ways that can be dangerous, even fatal. These reactions are involuntary and cannot be controlled by being told ‘not to panic’. They occur without your consent when your full body is immersed in cold water (not just your feet or head).
In general, the symptoms of cold water shock include:
- Hyperventilation and involuntary loss of breathing control
- Rapid heart rate
- Increased blood pressure
- Decreased dexterity
- Panic and impaired mental ability
In severe cases, cold water shock can also lead to:
- Unconsciousness
- Cardiac arrest
- Death
Symptoms of Cold Water Shock: Four Phases
The symptoms of cold shock can vary depending on the individual and the water temperature as well as the duration of exposure. There are four distinct stages, each characterized by different symptoms.
The Canadian Red Cross warns that the majority of cold-water immersion deaths occur during the first two stages, rather than from generalized hypothermia.
Stage One: Cold Water Shock (First 1 – 3 Minutes)
During this phase, the person experiences an involuntary gasp reflex, which can cause them to inhale water and drown. The gasp reflex is followed by severe hyperventilation, breathing 6-10 times faster than normal, which can lead to a decrease in carbon dioxide levels in the blood. This can cause the blood vessels in the skin to constrict, which can lead to an increase in blood pressure and heart rate.
The symptoms of this stage can lead to inhaling water, panic, vertigo and immediate drowning or heart failure.
Stage Two: Cold Incapacitation / Swim Failure (The Next 3 – 30 Minutes)
During this phase, the person may experience a decrease in muscle function and coordination, and a loss of sensation in the arms and legs, which can make swimming or staying afloat difficult.
Without being able to swim or hold onto flotation devices, a person may drown, even if they are a strong swimmer under normal conditions.
Stage Three: Hypothermia (30 Minutes to Several Hours)
During this phase, the person’s body temperature may drop to dangerous levels (below 35°C (95°F) and they may experience extreme fatigue, confusion, and disorientation. Finally, hypothermia sets in, and without rescue and proper first aid treatment, unconsciousness and death will follow.
Hypothermia can be a consequence of cold-water shock, but it is a separate condition which requires a special response and immediate medical attention.
Stage Four: Post-Rescue Collapse (During or After Rescue)
After being rescued, there is still a risk of death. A person’s blood pressure can drop suddenly upon leaving the water, as cold blood from extremities returns to the heart, potentially causing lethal heart rhythms. The person is at risk of experiencing cardiac arrest or fainting shortly after being removed from the water.
The 1-10-1 Rule
Safety experts use this simple formula to describe the stages of cold water immersion:
- 1 Minute: You have 60 seconds to get your breathing under control and avoid drowning from the initial shock.
- 10 Minutes: You have roughly 10 minutes of meaningful movement. After this, swimming failure occurs because the cold shuts down the muscles in your arms and legs.
- 1 Hour: You have approximately one hour before you lose consciousness due to hypothermia.
The fourth stage is not included in the 1-10-1 Rule.
How to Survive Cold Shock
If you fall into the water, all efforts should go to getting out of the water by the fastest means possible, usually via a reboarding device. Call for help with a VHF marine radio, as medical help will likely be necessary.
During Stage One, concentrate on avoiding panic and getting control of your breathing, if possible. Use the H.E.L.P. (Heat Escape Lessening Position) by pulling your knees to your chest and hugging them to protect high-heat-loss areas like the armpits and groin.
During Stage Two, it remains important not to panic. Swimming or treading water will greatly increase heat loss and can shorten survival time by more than 50%. Air trapped in clothing can provide buoyancy if you remain still in the water, and you can trust your PFD or life jacket to help keep you afloat also.
If you believe that rescue is imminent (within 10 minutes) and you have nowhere to go, you can cling to an overturned boat. If not, it is recommended that you attempt to swim to safety. It may be possible to swim up to roughly one kilometre in cold water. You must wait until your breathing has become regular before attempting to swim.
Always prioritize getting out of the water, even if it seems colder in the air.
During Stages Three and Four, it is vital to receive professional medical attention.
5 Tips to Avoid Cold Water Shock While Boating
It is important to do everything you can to avoid cold water shock. Many bodies of water in Canada are cold enough to cause cold water shock, even during the summer months.
- Always wear a PFD or their life jacket: it may save your life. If you fall into the water, it will keep your airways clear during the initial gasping stage, and provide flotation so that you do not have to tread water. It can also provide some extra protection and conserve your body heat.
- If you are navigating in cold waters, wear an immersion suit or an anti-exposure suit. These are usually one-piece suits that act both as a jacket to keep you warm and as a personal floatation device.
- Respect the capacity limits of your vessel to minimize the risk of capsizing.
- Keep a lookout to avoid running aground.
- Make sure you are qualified before engaging in any water sports or activities, including scuba diving.
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Frequently Asked Questions
Yes, Canadian waterways pose a significantly higher risk of cold water shock, because most Canadian waters remain cold year-round.
On a 30°C day in Ontario or BC, boaters often feel safe. However, the deep waters of the Great Lakes or the Pacific coast can still be 10°C–14°C. This massive gap between air and water temperature makes the body’s shock response much more violent.
In many parts of Canada (like the Maritimes or the North), the water temperature never actually leaves the High Risk zone, staying between 0°C and 10°C for the majority of the year.
Safety experts define cold water as anything below 21°C (70°F), and dangerously cold water as anything below 15°C (60°F). In Canada, even in July and August, many lakes and coastal areas barely reach these thresholds.
Most recreational boating fatalities in Canada occur in water below 15°C. At this temperature, the gasp reflex is total and uncontrollable.
No. The gasp reflex and muscle incapacitation happen so fast that even Olympic-level swimmers can experience swimming failure within minutes. The cold water impacts your body on a basic level and has nothing to do with how fit you are. A Life Jacket (PFD) is the only thing that keeps your mouth above water when your muscles stop working.
While it can happen in water as warm as 21°C (70°F), it becomes significantly more dangerous in water below 15°C (60°F). Most boating fatalities occur in water temperatures that many people would consider refreshing rather than freezing.
Focus entirely on keeping your head up and controlling your breathing, with minimal movement in your arms and legs. If you aren’t wearing a life jacket, roll onto your back and spread your arms and legs. Once breathing is controlled, use the H.E.L.P. (Heat Escape Lessening Position).
When a person is removed from cold water, cold blood from the extremities can rush back to the heart, causing a sudden drop in blood pressure or heart failure. This is known as Post-Rescue Collapse.
If you do not have access to immediate medical help, remove the wet clothing and provide dry blankets. Avoid providing excessive external heat, and concentrate on increasing internal heat (via warm high-energy drinks and food).
Sources
- Canadian Red Cross. Module 2 Ice & Cold Water Drownings and other water-related injuries in Canada 10 Years of Research. [PDF]. https://tc.canada.ca/sites/default/files/2024-03/tp_511e.pdf
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