This is a study on the nature of Hipotermia, that is on the abnormal cooling of the body temperature that can also be fatal. It is a risk that often occurd in water sport and adventurous enterprieses. The film describes the difficulites faced by a group of kayak enthusists on a cold day that they spent descending a river in a wild environment. The body movements of these sportsmen, the causes of hypotermia, its first symptons and the measures of prevention and cure are described.