Aysen fjord is one of the natural connections between the Andean mountains and the system of islands and fjords in southern Chile, called the Chilean Inland Sea. In this fjord, several extreme events take place which make it special from an oceanographic point of view: very large river discharges fed by rain and by melt water from the Andes glaciers accompanied by low temperatures provoking a very sharp gradient in the vertical density structure of the system. This feature is very important for the functioning of the system from the hydrodynamic and the ecological point of view.