Winter swimming

Cold, movement and open water

Winter swimming combines the cold stimulus with movement in lakes, rivers or the sea — usually at water temperatures below 10 °C, often close to freezing. That makes it the most demanding form of cold training: on top of the cold shock come currents, waves, poor visibility, slippery entry points and the fact that help in open water is not instantly at hand. Anyone who wants to swim in winter should be a confident swimmer, have spent weeks with cold showers and baths beforehand, and join an experienced group.

The biggest risks

Research on cold-water immersion — above all the work of British physiologist Mike Tipton — describes two phases in which it gets dangerous. In the first minute, cold shock triggers an involuntary gasp and hyperventilation; inhaling water at that moment can lead to drowning long before the body cools down. Then arms and hands cool: from around three minutes – even sooner in near-freezing water – they can lose strength and become clumsy, typically somewhere between 3 and 30 minutes, even while your head still feels clear. So there is no safe time window, only a risk that grows with every minute — until you can no longer swim. True hypothermia only comes later: in cold water, drowning is the bigger risk than freezing.

Then there is the afterdrop: after you get out, your core temperature keeps falling for a few minutes. Dizziness or heavy shivering that only start on the shore are therefore typical — and a reason to stay warmly dressed until they pass.

What speaks for it

Many winter swimmers report better mood, less stress and a strong sense of community. Observational studies show good cold adaptation and in part favourable metabolic markers in regular winter swimmers. Whether that is down to the cold itself, to exercising outdoors, or to healthier people being the ones who swim in winter in the first place cannot be told from these data — a review by Espeland et al. (2022) therefore explicitly calls the evidence inconclusive.

Progression

• Start in autumn: begin in September or October and follow the falling water temperature instead of starting in January.
• Just dip at first: for a few weeks, go in, stay 30 seconds to two minutes, get out again.
• Then short distances parallel to the shore, within sight of the exit, for a few minutes.
• Increase time only slowly and keep it shorter again on colder days.

Safety

• Not medical advice. With heart or circulation conditions, heart rhythm disorders, high blood pressure, Raynaud's syndrome, epilepsy, cold urticaria or during pregnancy, check with a doctor first.
• Never go in alone — at least one person on the shore who keeps an eye on you and knows what to do in an emergency.
• No alcohol, neither before nor afterwards "to warm up".
• No diving in head first, no breath-holding, no breathing exercises in the water. Hyperventilating or diving under in cold water can make you lose consciousness.
• Get out at the first warning signs: shivering, numb or clumsy hands, dizziness, slowed thinking.
• Warm up gradually: dry, warm clothes, a hat, a warm drink, light movement — not straight into a hot shower or the sauna.
• Stay off the ice: never walk on frozen water or swim under an ice sheet; check entry points for slippery surfaces.