Baltic Sea

Shallow sea, and arm of the Atlantic Ocean, extending northeast from the narrow Skagerrak arm of the North Sea and the Kattegat strait, between Sweden and Denmark, to the Gulf of Bothnia between Sweden and Finland. Its coastline is 8,000 km/5,000 mi long; the sea is 1,500 km/930 mi long and 650 km/404 mi wide, and its area, including the gulfs of Riga, Finland, and Bothnia, is 422,300 sq km/163,000 sq mi. Its average depth is 65 m/213 ft, but it is 460 m/1,500 ft at its deepest.

Its shoreline is shared by Denmark, Germany, Poland, the Baltic States, Russia, Finland, and Sweden.

Many large rivers flow into the Baltic Sea, including the Oder, Vistula, Niemen, Western Dvina, Narva, and Neva, draining an area covering one-fifth of Europe. Tides are hardly perceptible, and salt content is low, decreasing towards the Gulf of Bothnia. The sea bed consists of mud or hard clay in the deeper areas, with sand and shingle on shallow banks and coasts. Navigation is often made dangerous by its narrowness, shallowness, and sudden storms. Most ports are closed by ice from December until May; the sea is recorded to have frozen completely only twice, in 1658 and 1809. The Kiel canal links the Baltic and North seas, and the Göta canal connects the two seas by way of the southern Swedish lakes. Since 1975 the Baltic Sea has been linked by the St Petersburg–Belomorsk seaway with the White Sea. A waterway system links the Baltic Sea (at St Petersburg) with the Caspian Sea (at Astrakhan). The currents in the Baltic generally flow anticlockwise, southwards along the Swedish coast.