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.

波罗的海属大西洋海域，是欧洲北部内海。波罗的海长约1，600公里，面积约38. 6万平方公里，它被瑞典、丹麦、芬兰、爱沙尼亚、拉脱维亚、立陶宛、俄罗斯、波兰和德国所环绕。

波罗的海是其周边国家货物运输的主要航道，这些货物主要是俄罗斯、芬兰和瑞典的木材，瑞典的铁矿石，波兰的煤，还有鱼类。但是波罗的海的航运并不是很通畅，一个原因是很多港口水深不够。重量级船舶无法停靠;另外一个原因是有不少淡水河流入波罗的海，造成该海的含盐度较低，冬季容易结冰。