I recently had the experience of swimming in a lido in the UK, which is an outdoor swimming pool. This proved to be an interesting experience, as the pool was unheated with a water temperature of around 15°C (41°F) and an air temperature of around 16°C (61°F).
Trying to get my money’s worth, I spent over an hour in there and I never really warmed up, which made me wonder, how long should you stay in cold water?
The time it takes for hypothermia to develop in a swimmer depends on the temperature of the water and the warmth protection of the swimmer. You should treat any water below 21°C (70°F) with caution. Water temperature less than 5°C (41°F) can result in death in under 20 minutes.
Thankfully, I knew what to expect from swimming in 15°C (41°F) as I had a lot of exposure to this water temperature in the past from swimming in my cold backyard pool, but if I did not know what I was doing this lovely day out could have turned to disaster very quickly.
In this article, I will dig deeper into what to expect from cold water and how to swim in cold water safely, covering:
- How cold is too cold to swim?
- How long should you stay in cold water?
- What is cold water shock?
- What is hypothermia?
- What is afterdrop?
- Signs you should stop swimming in cold water
- What to wear to keep warm in cold water
How Cold Is Too Cold To Swim?
Swimming in cold water is an exhilarating thing. At first, the cold is a shock and you wonder what on earth you are doing, but once you acclimatise and find an enjoyable place to swim, it is an activity millions of swimmers complete every day.
As a beginner, you may have seen cold water experts swimming in ice water, but as a novice, it is important to understand that cold water is dangerous and can be deadly.
Before starting your cold water adventure, it is essential to know your water temperatures and what temperature is considered too cold to swim.
Although there is no universal definition of cold water, treat any water temperature that is less than 21°C (70°F) with caution. Water temperature between 10°C-15°C [50°F-59°F] is dangerously cold and maximum cold water shock happens in this region. Water temperature below 5°C (41°F) is exceptionally dangerous and painful.
Below is a table showing water temperatures in both Celsius and Fahrenheit and how the National Centre For Cold Water Safety classify the different water temperatures. [source]
| Cold Water Temperature | Water Feels Like |
|---|---|
| 30°C – 40°C [86°F – 104°F] | This water temperature is pleasant. |
| 25°C – 30°C [77°F – 86°F] | This water temperature feels cool. |
| 20°C – 25°C [68°F – 77°F] | This water temperature is classified as cold. Our breathing is affected in this region. |
| 15°C – 20°C [59°F – 68°F] | Below 21°C (70°F) should be treated with caution. We are entering the region of dangerous cold according to the National Centre For Cold Water Safety. |
| 10°C – 15°C [50°F – 59°F] | This water temperature region is very dangerously cold. Many will find this region painful. You will suffer from maximum cold shock in this region. |
| Below 5°C [50°F] | Below this region is exceptionally dangerous and painful. Only the very experienced should swim in this cold water temperature. |
For those of you who already know your water temperatures, you may think that the recommendation to treat any cold water below 21°C (70°F) with caution as being overly safe.
Although many fit and healthy swimmers take their first cold water dip in water around 15°C – 20°C [59°F – 68°F], the National Centre For Cold Water Safety explains that they have picked 21°C (70°F) as a cautionary number for the following reasons: [source]
First, our breathing is negatively affected in water below 25°C (77°F).
Second, for first-time cold water swimmers who are not acclimatised, the symptoms of cold water shock reach a maximum intensity between 10°C – 15°C (50°F – 60°F).
In 1983, the US Coast Guard formally defined cold water as anything below 60F (15C), but as the result of a 1998 Congressional inquiry, they subsequently raised it to 70F (21C). The American Canoe Association (ACA) sets their thermal protection threshold at 60F (15C), and another paddling organization, American Whitewater (AW) recommends 50F (10C).
National Centre For Cold Water Safety
How Long Should You Stay In Cold Water?
It can take so much willpower and effort to get into cold water, there is a temptation to stay in there for as long as possible to make the effort worth it.
But how long is too long to swim in cold water?
It is really difficult to give an exact time for how long you should stay in cold water as this will depend on your own personal tolerance and the actual temperature of the water.
As a general rule for moderately cold water, if you are still cold after 10 minutes it is time to get out and warm, however, the length of time you stay in cold water also depends on the water temperature and the protective gear you are wearing. Often, it is better to take a quick dip, especially if in doubt.
Perhaps a better approach is to understand when hypothermia will set in. Again, this varies depending on the swimmer, the water temperature, and the cold water protection they are wearing.
According to the RNLI, it can take as long as 30 minutes for hypothermia to set in, even in very cold water. [source]
The British Canoeing Association has created a wonderful information sheet about hypothermia and the effects of cold water immersion. [source]
Here is a brief summary of what the British Canoeing Association recommends. You can download this full information sheet here. [source]
| Water Temperature | Loss Of Dexterity | Time To Exhaustion / Unconsciousness | Expected Survival Time |
|---|---|---|---|
| 0°C (32°F). | Less Than 2 Minutes | Up To 15 Minutes | Less than 15 – 30 Minutes |
| 0°C-4°C (32°F-39.2°F) | Less Than 3 Minutes | 15 – 30 Minutes | 30 – 60 Minutes |
| 4°C-10°C (39.2°F-50°F) | Less Than 5 Minutes | 30 – 60 Minutes | 1 – 3 Hours |
| 10°C-16°C (50°F-60.8°F) | 10 – 15 Minutes | 1 – 2 Hours | 1 – 6 Hours |
| 16°C-21°C (60.8°F-69.8°F) | Up To 40 Minutes | 2 – 7 Hours | Up To 40 Hours |
What Is Cold Water Shock?
Cold water shock happens to the body when first entering cold water.
Cold water is dangerous, and our body undergoes stress when exposed to cold water.
Typically, maximum cold water shock intensity happens below 15°C [59°F]. [source]
When you first enter cold water, the contact of the cold water on your skin will cause your blood vessels to contract. This creates resistance to blood flow, meaning that your heart will have to work harder, resulting in an increase in blood pressure.
Great care must be taken as this can cause heart attacks, even in the healthy. [source]
In addition, your breathing will be affected, as the cold impact on your body will cause you to gasp. Your breathing rate will increase as a result, and for some, this can lead to panic.
How To Reduce The Risk Of Cold Water Shock
1. Go Slow
Approach the cold water slowly and with caution. By taking things slowly, you reduce the risk of panic setting in and gasping, which can lead to inhaling water. Inhaling water is exceptionally dangerous. As little as half a pint of water in the lungs can result in drowning for a fully grown man. [source]
Slowing walk into the water with your hands in the water. There is no need to submerge your head until you are ready.
2. Wait One Minute
The initial effects of cold water shock do pass, but you must be patient and wait. Typically, it can take around one minute for the initial effects of cold water shock to pass.
Many strong swimmers try to fight cold water shock by swimming. This can be a fatal mistake.
Professor Mike Tipton MBE, who is a Professor of Human and Applied Physiology at the University of Portsmouth, identifies cold water shock as one of the greatest threats to life.
Our instinct is to thrash around and fight when suddenly dropped in cold water. Professor Mike Tipton recommends you resist the urge to fight (the fight-or-flight reflex), turn on your back and float until the initial cold water shock passes. [source]
The cold water will make you gasp uncontrollably and it is important to let this phase of cold water shock pass before attempting to swim.
I have covered the effect of cold water shock on good swimmers in greater detail in this article, How Can Good Swimmers Drown? (Here’s what to know)
3. Float To Live
If you unexpectantly fall into cold water, the official advice is to flip onto your back and float.
Again, this is to keep your airways clear as you gasp uncontrollably.
The Royal National Lifeboat Institution has a fantastic, life-saving campaign called “float to live”, which explains what you should do in an emergency water situation.
You can read more about how to float on the Royal National Lifeboat Institution website.
What Is Hypothermia?
Hypothermia occurs when your body drops below 35°C (95°F) [source]
According to the RNLI, it can take as long as 30 minutes for hypothermia to set in, even in cold water.
Some signs of hypothermia include:
- Shivering
- Cold, dry and pale skin
- Skin and lips may be blue
- Speech is slurred
- Breathing is slow
- Tired and confused.
It is important to always take precautions to ensure the body never gets that cold.
In particular, it is important to cold water swim with a buddy, to ensure someone is watching your back and get you to safety if you find yourself in a situation where hypothermia is a risk.
To learn more about hypothermia and what to do if you encounter someone who has the signs of hypothermia, check out the NHS health website. [source]
What Is Afterdrop?
When you leave the cold water, your body will continue to cool despite being out of the water. This phenomenon is known as afterdrop.
Afterdrop is just as dangerous as hypothermia.
The American Heart Association defines hypothermia as the point where body temperature is less than 36.0°C [96.8°F].
Afterdrop, is defined as continued cooling following removal from cold stress. [source]
Afterdrop may not be noticeable at first. You may find yourself dried and changed into dry clothes and then notice that you are still very cold. It can take up to five minutes after exiting the water for the effects of afterdrop to be noticeable. [source]
Afterdrop will continue, i.e. your body temperature will continue to drop until your core temperature starts to rise again.
It is very important to be mindful of afterdrop, as the dangers of cold water extend beyond the swim.
Poor muscle control and a lack of ability to think clearly can be experienced as your core temperature continues to drop. Therefore, having a swimming buddy who can help is essential when venturing into cold water.
A study completed on 11 swimmers who participated in the New Year’s Day Alcatraz Swim with an open water temperature of 11.7°C [53.0°F] found the following: [source]
- Hypothermia was seen in 5 of the 11 subjects.
- Afterdrop was seen in 10 of the 11 subjects.
These results suggest that hypothermia and afterdrop can occur commonly after recreational open water swimming. [source]
The study concluded that participants should be “observed for signs of temperature decrease following removal from cold stress”. [source]
To handle the effects of afterdrop, warm up slowly and gradually. [source]
Here are some things you can do after your swim to minimise the effects of afterdrop:
- Don’t hang around after your swim. Get dressed immediately.
- Wear plenty of layers, including jumpers, jackets, hats, gloves and even a thermal blanket to trap the heat.
- Drink something warm (I find something sugary like chocolate also helps).
- Get to a warm place.
- Do some light movements to generate body heat.
Hypothermia is deadly and you should take any symptoms of hypothermia seriously.
I am a swimmer, not a doctor, so I recommend you use high authority medical sites to learn to identify the signs of hypothermia.
Here are some links to high authority medical websites who discuss hypothermia in greater detail and can help you identify when someone is hypothermic.
Signs You Should Stop Swimming In Cold Water
It is tempting to stay in cold water as long as possible, but you should always be mindful when in cold water and get out after 10 minutes if you have not warmed up.
Here are some signs that you can watch out for which will tell you it is time to leave:
1. Cold After 10 Minutes]
If you cannot warm up and still feel cold and uncomfortable after 10 minutes, then it is safest to get out. Your body temperature will continue to drop, so it is safest to get out while you can and warm up.
2. Difficulty Speaking
How well you can speak indicates your condition on the water.
First, if you mumble or slur your speech, this is a serious sign of hypothermia. Anyone who slurs their words needs to exit the water immediately.
Second, cold water will make you gasp. If you are struggling to hold a conversation after the initial cold water shock has passed, it is safest to exit the water until you can control your breathing.
3. Weakness In Limbs
It is much harder to swim in cold water as your limbs will feel heavy.
If you experience heaviness or weakness in your limbs, it is time to exit the water, as this condition will get worse.
4. Uncontrollable Shivering
Shivering is part of being cold, but if you find yourself uncontrollably shivering, it is time to exit the water.
We will all shiver in cold water, but violent shivering can be a sign of hypothermia.
5. Loss Of Coordination
A loss of coordination is a sign of hypothermia. You should always have good coordination in the water. If you feel a loss of coordination, call for help or get out immediately.
You may find your swimming stroke is not optimal or you are swimming differently, then it is time to get out.
6. Loss of Dexterity
Extreme exposure to cold water will induce numbness and a loss of dexterity in the fingers. If your limbs feel numb and you experience a loss of dexterity, exit the water immediately.
As already mentioned, it is important to be able to spot the signs of hypothermia while cold water swimming. For more details on how to sport the signs of hypothermia and how to recognise if you are becoming hypothermic, check out this great article from The Outdoor Swimming Society.
What To Wear To Keep Warm In Cold Water?
Although many cold water swimming purists will want to keep their swimming gear to a minimum to feel the full impact of the cold, there are garments and accessories on the market to help take the sting out of cold water.
This gear can help you enjoy the cold water experience for longer.
1. Neoprene Gloves
Keeping your hands warm can go a long way in helping you brace for the cold.
Wetsuit gloves come in a range of thicknesses; typically, 2mm, 3mm and 5mm. The thicker the gloves, the warmer they are.
For example, a 2mm wetsuit glove is perfect for summer. A 5mm wetsuit glove is ideal for winter.
Although the thicker the glove the warmer personally, I find you lose some water feel in thicker gloves. Therefore, despite the cold, I opt for a thinner glove (3mm) just to give me a better feel of the water.
2. Neoprene Hood
Keeping my head warm really helps in cold water.
A neoprene hood is a wonderful way to protect the head from the cold if you do not want to wear a full wetsuit.
Just like neoprene gloves, neoprene hoods come in a range of thickness from 2mm to 5mm.
Personally, I have a 3mm neoprene hood that takes the edge off in cold water and reduces the impact of “ice-cream head”.
3. Neoprene Socks
When my feet are cold I cannot warm up, therefore I use neoprene socks when cold water swimming.
Not only does this protect the feet when walking to the water, but it also takes the sting out of the cold water and protects our extremities.
Again, I like a 3mm thick neoprene sock as I find that 5mm (although the warmest) is just too thick to get a feel for the water. I feel far too restricted in 5mm neoprene.
4. Neoprene Rash Vest Or Thermal Jacket
Neoprene rash vests are similar to regular rash vests but are made from neoprene, which is thicker and warmer.
Sometimes, light neoprene rash vests may just have one panel (for example, the front core) made from neoprene.
This is a wonderful compromise when cold water swimming if you want some warmth protection but do not want to cover up completely in a wet suit.
To be honest, I have found neoprene rash vests hard to find, and I searched high and low before finding my own, which is a regular rash vest, but the front panel is made from 2mm neoprene. I wish I could post a link, but it is no longer available.
To ensure that you are purchasing a neoprene rash vest and not just a regular vest check that the word “neoprene” is used in the description and a thickness is specified.
There should be some reference to thermal protection.
Alternatively, it is worth searching for a thermal rash vest or thermal rash guard, as these words can be used interchangeably.
Using a thermal neoprene rash vest is a great way to get some warmth protection without having to wear a full wetsuit.
Here is an example of a 2mm neoprene jacket for women that can help keep you warm without having to wear a full wetsuit:
5. Wetsuit
Sometimes the water is just too cold and a full-body wetsuit is needed.
Although I like to avoid a full wetsuit in order to get as much contact with the water as possible, when the water is too cold, it is safest to wear a wetsuit.
When choosing a wetsuit for cold water, check the temperature of the water you are swimming in and then match the thickness of the wetsuit to the swimming temperature.
The standard thicknesses available for wetsuits are typically 2mm, 3mm and 5mm.
As a general rule, 2mm and 3mm wetsuits are suitable for warmer water and 5mm for colder water.
Personally, I like to get a wetsuit with 3mm on the arms and then 5mm in the core or trunk of the suit. This allows my arms to move freely but my core temperature is well protected with 5mm neoprene material.
When purchasing a wetsuit for swimming, it is important to be aware that different wetsuits have different designs based on the sport. For example, wetsuits for swimming should have excellent mobility on the shoulders.
Orca produces some great wetsuits that are suitable for open water swimming.
Final Thoughts
Cold water swimming is a wonderful experience, but it is important to listen to your body and if you start to feel too cold, then get out of the water. As a general rule, if you are still cold after 10 minutes, it is time to get out.
Before entering the world of cold water swimming, it is important to know what is defined as cold water so you know what to expect and understand the risk level involved.
The National Centre For Cold Water Safety suggests that any water with a temperature of less than 21°C (70°F) should be treated with caution.
In addition, knowing what cold water shock, hypothermia, and afterdrop are is essential to continuing to swim safely in cold water.
Know your limits and never take risks. Cold water swimming is a wonderful experience, but it can be deadly and great caution with cold water understanding is needed to complete it safely.
Happy swimming!