Gulf of Bothnia

Gulf of Bothnia, arm of the Baltic Sea, between Finland on the east and Sweden on the west. It is about 645 km (400 mi) long and between 80 and 240 km (50 and 150 mi) wide. The Ahvenanmaa (Åland) islands are generally regarded as the dividing line between the Baltic proper and the Gulf of Bothnia. Many rivers from Sweden and Finland empty into the gulf, reducing the salinity of the gulf water. In winter it is usually frozen. Rauma, one of the oldest harbours in Finland and a UNESCO World Heritage Site since 1991, is situated on the eastern shore of the Gulf. In 2000 the High Coast in the south of the gulf was designated a UNESCO World Heritage Site because of its unique geological features.