The Baltic Sea is an enclosed sea, covering an area of 386, 000 square kilometers in northern Europe. It is bordered by Sweden and Denmark on the west, Finland, Estonia, Latvia, Lithuania and Russia on the east, and Poland and Germany on the south.

The Baltic Sea is the most important channel to transport the cargoes of these countries. Nowadays the chief cargoes shipped across the sea are timber from Russia, Finland and Sweden, iron form Sweden, coal from Poland, and fish. The transportation in the Baltic Sea has never been easy. Many of its harbors are too shallow for the larger ships. The water of the Baltic is not very salty because many fresh rivers flow into it, so it freezes more easily. Many of its ports are blocked by ice in winter.

波羅的海屬大西洋海域，是歐洲北部內海。波羅的海長約1，600公里，面積約38. 6萬平方公里，它被瑞典、丹麥、芬蘭、愛沙尼亞、拉脫維亞、立陶宛、俄羅斯、波蘭和德國所環繞。

波羅的海是其周邊國家貨物運輸的主要航道，這些貨物主要是俄羅斯、芬蘭和瑞典的木材，瑞典的鐵礦石，波蘭的煤，還有魚類。但是波羅的海的航運并不是很通暢，一個原因是很多港口水深不夠。重量級船舶無法?？?另外一個原因是有不少淡水河流入波羅的海，造成該海的含鹽度較低，冬季容易結冰。