Winter swimming: embrace the chill, but stay safe

Why you need to consider the whole experience, not just your time in the water

Winter swimming is an odd activity: exhilarating and accessible but with easy-to-overlook dangers. The risks are manageable, but as it gets colder, your margin for error narrows. The difference between a great swim and a disaster could be just a few extra minutes in the water or too much time faffing when you get out.

Understand what makes you cold

Multiple factors determine how quickly you get cold. Water temperature is crucial. In shallow inland waters, the temperature can change rapidly. For example, the Thames where I swim recently dropped from 10.5 to 7.0 degrees in two days, significantly affecting how quickly I got cold. Other factors, both external and internal, also make a difference. A cold wind will chill you before you even get in the water and make it harder to warm up afterwards. If you’re unwell, hungover, hungry, stressed, or sleep-deprived, these will also impact your swim.

Why you need a safety margin

Remember, a winter swim isn’t over until you’ve dried, dressed, and warmed up. Factor in how long it will take you to get in and climb out again. The total time it takes to do all these things determines how cold you get, not just your time in the water. Everything has a knock-on effect. If you spend too long getting into the water, you will have less time to swim. If you get too cold in the water, you will struggle with dressing and get even colder.

To stay safe, give yourself a big margin for error. For example, if you think your maximum time for a safe swim (including pre-swim faff, entry, swimming, exit, drying, and dressing) is 20 minutes, try to do it all in 10. Because of the many factors affecting how quickly you get cold, it’s not possible to be precise about safe exposure times to cold water. What is fine one day may be too much on another similar but subtly different day. It’s best to be cautious.

We’ve created two infographics to demonstrate this.

In general, the warmer the water, the longer you can safely swim. So far, so obvious. But what’s less apparent is that if you get it wrong in warmer water, you have more time to recover the situation. For example, if you can swim comfortably for 90 minutes in warm water and you swim an extra 15 minutes, this probably won’t tip you into hypothermia. However, if 15 minutes is your limit in cold water, you could be in a lot of trouble if you add an extra 15 minutes. The gap between a safe swim and a dangerous one narrows in the cold.

In this second chart, we’re looking at all the activities linked to your swim. When it’s cold, you need to cut your time in the water. We all know that. The point here is that you may need to shorten your swim more than you think and allow more time for faff and changing.

Remember, you get most of the benefits from winter swimming in the first couple of minutes. Why increase the risks when there is nothing else to gain?

Explore more about cold water swimming on our website.