In the resort town of Skagen we can watch an amazing natural phenomenon. The city is the northernmost point of Denmark, where the Baltic Sea and the North Sea meet. The two opposite pairs in this place can not join because they have different densities and salinity. The area where the Baltic Sea and the North Sea meet is quite shallow so that the contact surface is relatively small. Of course there is some mixing but very minimal. This is also helped by the fact that the Baltic is not the tide that keeps most of its water in the Baltic basin and this water is constantly reduced by its salinity flowing into the Baltic. Were it not for a small hole into the North Sea, the Baltic would be a giant freshwater lake.
