An icy swim could have significant health benefits, including reducing body fat and the risk of diseases such as diabetes, according to a review.
Some 104 studies were examined by researchers, who found that many reported major health benefits from cold water swimming, including on good fat which helps burn calories.
This could help prevent obesity and cardiovascular disease, but the researchers said overall health benefits were unclear.
The review indicated what appears to be a positive link between cold water swimming and brown adipose tissue (BAT).
BAT is a good body fat that is activated by the cold, burning calories to maintain the body's temperature.
It is different to "bad" white fat which stores energy.
Repeated icy swims could significantly increase insulin sensitivity and decrease insulin concentrations, the study found.
Researchers from UiT The Arctic University of Norway and from the University Hospital of North Norway completed the study, which is published in the International Journal of Circumpolar Health.
A lot of the available research involved small numbers of people, often of one gender, and with different water temperature and levels of salt, the researchers said.
And it is unclear whether or not winter swimmers are naturally healthier, they added.
Lead author James Mercer, from UiT, said: "From this review, it is clear that there is increasing scientific support that voluntary exposure to cold water may have some beneficial health effects.
"Many of the studies demonstrated significant effects of cold-water immersion on various physiological and biochemical parameters.
"But the question as to whether these are beneficial or not for health is difficult to assess.
"Based on the results from this review, many of the health benefits claimed from regular cold exposure may not be causal.
"Instead, they may be explained by other factors including an active lifestyle, trained stress handling, social interactions, as well as a positive mindset.
"Without further conclusive studies, the topic will continue to be a subject of debate."
The researchers warned that swimming in icy water also carries risks, such as hypothermia, and heart and lung issues related to the shock of the temperature.