Winter swimming is the activity of swimming during the winter season, typically in outdoor locations (open water swimming) or in unheated pools or lidos. Many winter swimmers swim with standard swimming costumes rather than with wetsuits or other thermal protection. The activity may or may not involve freezing water, depending on the geographical location and the local temperature. Famous winter swimmers are Lynne Cox and Lewis Gordon Pugh.
Ice swimming is swimming in a body of water with a frozen crust of ice, and may be synonymous with winter swimming in colder countries. This requires either breaking the ice or entering where a spring keeps the water from freezing over. This may also be simulated by a pool of water at 0 °C, the temperature at which water freezes.