Large shallow arm of the North Sea, extending NE from the narrow Skagerrak and Kattegat, between Sweden and Denmark, to the Gulf of Bothnia between Sweden and Finland. Its coastline is 8,000 km/5,000 mi long, and its area, including the gulfs of Riga, Finland, and Bothnia, is 422,300 sq km/163,000 sq mi.
Its shoreline is shared by Denmark, Germany, Poland, the Baltic States, Russia, Finland, and Sweden.
Many large rivers flow into it, including the Oder, Vistula, Niemen, Western Dvina, Narva, and Neva. Tides are hardly perceptible, and salt content is low; weather is often stormy and navigation dangerous. Most ports are closed by ice from Dec until May. The Kiel canal links the Baltic and North seas; the Göta canal connects the two seas by way of the S 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) to thge Caspian Sea (at Astrakhan).