Claire’s* legs ache with cold as she pushes forwards into the messy grey sea, grey sand stretching behind her, grey sky above. She braces herself against each incoming wave, the wind whipping at her exposed skin. Her local beach, Scheveningen, on the western coast of the Netherlands, is a wide expanse of sand running uninterrupted beside the North Sea. It’s March, and the sea temperature is about 6°C.
In the water, Claire’s skin temperature drops instantly, and after a few minutes, her muscles start to cool, stiffening like chewing gum. Her swim is short, and warming up takes hours, but she’s elated to be there. “We were jumping around, shrieking like schoolgirls,” she says, remembering her first taste of cold water swimming. Claire needed the boost, as three months before,…