Thus, I believe that the basis for analysing and managing marine recreational activities, including tourism, must be ensuring the sustainability of the resource upon which depend, not only the recreation, but the health of all living things. This may seem to be somewhat of an over-reaction. The sea is vast and by far the great majority of marine-based tourism occurs in but a small portion of that vastness. How then can recreational activities in the sea threaten the survival of the planet? This question is addressed in a reflection from one of the best-known of ocean explorers, Jacques Cousteau