The Rhine river has its source in canton Grisons, fills Lake Constance and ends in the North Sea. Popular diving sites are the old Rhine at Diepoldsau and the customs bridge at Rheinau. Although one usually encounters eels in this river, this species is unfortunately going to extinct. The eels have to travel from the european rivers across the Atlantic ocean to the Sargasso sea for breeding. But between Lake Constance and Basel there are already eleven hydraulic power stations and in each of those about one third dies in the turbines. So almost no eel has ever a chance to reproduce.