Background
An increasing volume of anecdotal and scientific evidence suggests that mood may be enhanced following swimming in cold water. The exact mechanisms responsible are largely unknown, but may include the effects of exercise from swimming and the effects of cold. This study examined the effect on mood following immersion in cold water, where swimming was not the primary activity.

Methods
The Profile of Mood States (POMS) questionnaire was completed by 64 undergraduate students. The following week, 42 participants completed up to 20-min immersion (18ʹ36ʺ ± 1ʹ48ʺ) in cold sea water (13.6°C). Twenty-two participants acted as controls. The POMS was completed immediately following the cold-water immersion by both groups.

Results
The cold-water immersion group showed a significant decrease, with a large effect size, of 15 points from 51 to 36, compared to 2 points in the control group, 42 to 40. Positive sub-scales increased significantly in the cold-water immersion group (Vigour by 1.1, and Esteem-Related Affect by 2.2 points) and negative sub-scales showed significant reductions (Tension by 2.5, Anger 1.25, Depression 2.1, Fatigue 2.2, and Confusion 2.8 points). The control showed no significant change except for depression, which was significantly higher after the period by 1.6 points.

Conclusion
Cold-water immersion is a well-tolerated therapy that is capable of significantly improving mood in young, fit, and healthy individuals. A key aim of this study was to control for the effects of swimming as a mechanism responsible for the improvement in mood which has been shown in previous studies. Thus, the change in mood evidenced in this study was not due to physical activity per se. Consequently, the hypothesis that cold in and of itself can improve mood is supported.