Bothnia, Gulf of

Northern arm of the Baltic Sea, about 650 km/404 mi long and 70 km/43 mi wide at its narrowest point. The Åland Islands are to the south, Finland to the east, and Sweden to the west and north. Much of the gulf is less than 100 m/328 ft deep, and navigation is impeded by sandbanks and small islands. Numerous rivers flow into the gulf, and salinity is low. In winter the whole surface is generally ice-bound. There are ferry routes between Sweden and Finland.