An inland sea of northern Europe, the Baltic is nearly 1,600km in length. It lies between Sweden on the west, Finland and the former USSR on the east, and Poland and Germany on the south. It has three main gulfs - the Gulf of Bothnia, the Gulf of Finland and the Gulf of Riga. Navigation in the Baltic has never been easy. The Danish channels and many of the harbours are too shallow for larger ships and wide areas are regularly frozen over for two months of the winter.