- Cold shock: this is the body’s reaction to sudden cold. It begins with the gasp reflex and continues with uncontrolled hyperventilation. This is a good reason not to jump into water unless it’s over 15°C or you’re acclimatised.
- Cold incapacitation: this happens when you get too cold. You get in, and after a couple of minutes of feeling uncomfortable the water feels pleasant. As a novice swimmer, or even as a strong swimmer with limited experience of swimming outdoors, you then attempt to cross the lake, but half way across start feeling cold again. Your body continues to lose heat, blood shunts to the core to keep organs warm. Your muscles lose power, limbs become slow and heavy, and swimming becomes increasingly difficult. This is cold incapacitation and it can all-too-easily lead to drowning. A further effect of cold incapacitation is the loss of coordination we all suffer as we become cold. The bank that previously seemed a safe exit point might now be difficult or even impossible for you to climb as you struggle to grip with your hands, while your limbs are clumsy and numb.
- Cramp: cramp can strike anywhere, and some people are more prone than others. If you’re cold, cramp is perhaps more likely. If you do cramp, float on your back and call for help.
- Asthma: in some asthmatics, cold can trigger an attack.
- Cold water urticaria: Allergic urticaria on leg in the form of hives induced by cold. Cold urticaria (essentially meaning “cold hives”) is a disorder where hives (urticaria) or large red welts form on the skin after exposure to a cold stimulus. The welts are usually itchy and often the hands and feet will become itchy and swollen as well.
- Hypothermia: contrary to popular opinion hypothermia is unlikely to cause a swimmer to get into difficulties since it will take some time to become truly hypothermic; cold incapacitation and cold shock are the main culprits. Be aware that when you get out of the water and begin to warm up, warm blood from your core will cool quite fast as the peripheral blood vessels open up. This is the point where swimmers experience sudden coarse shivering (known as after drop – it’s the body’s attempt to generate heat).
As a general rule, get expert medical advice before winter swimming if you have a heart condition, high blood pressure, asthma, or are pregnant. Swim sober, and avoid cold water if you have a hangover. However, thousands of people swim outdoors safely every year, and even more survive festive dips – one off jumps into the water – with mountainous goosebumps to show for it. If you’re otherwise fit and healthy and work on understanding how your body reacts to cold water you can mitigate the risks.