This article studies the organization of a team of kayakers with special emphasis placed on socially constructed risk taking in navigation on a torrent such as the Ubaye. The question of involvement is raised all the more acutely as it implies the physical integrity of the practicers. These are indeed virtually self-reliant owing to site isolation. The author tries to determine the steps that enable to regard upper river kayaking as an activity depending on a singular collective organization. The description of the rules, namely the safety rules, that govern social relations within this collectivity reveals the foundations of this activity. By showing that risks inherent to upper river kayaking are accepted within a social framework and, as a result, that kayaking down a river is a shared experience rather than the staging of individual behaviours this ethnographic study helps apprehend what is involvement in a risky sport.