Political map of the Baltic Sea and surrounding areas
Topography of the Baltic Sea Area. The plains (in green) were formed during the last Ice Age.
Ten thousand years ago, the ocean what we know today as the Baltic Sea was, in fact, a formidable inland sea, with only a few connections to the Atlantic Ocean by two or three rivers.
Nobody knows what the sea was called then, but scholars of today named it the Ancylus Lake. The lake's water was the remains of several stages of the retreat of the melting Scandinavian ice sheet following the last glacial period we all know as the Ice Age.
Some thousand years later the sea became a branch of the Atlantic Ocean and a popular tourist destination, the Baltic sea is today connected to the North Sea (a branch of the Atlantic Ocean itself) via the Kattegat and Skagerrak Straits, enabled Vikings of past times just as cruise ships of today to roam the seas for business. In the 13th to the 15th century, the region was one of the main playgrounds and the commercial core of the Hanseatic League (Hanse), a confederation of merchants and city unions which became an economic and political power in Northern Europe.
The Baltic Sea is known by a variety of names, the Germans call it Ostsee (East Sea), the Swedish Östersjön, in Danish it's Østersøen, in Russia it is known as Baltiyskoye More, in Finland as Itämeri, for the Polish people it is Morze Bałtyckie, and in Estonia the 'East Sea' is known as Läänemeri (West Sea).
The Baltic Sea (including the Gulf of Bothnia and the Gulf of Finland) covers an area of 377,000 km2 (146,000 sq mi)
making it somewhat larger than Germany or slightly smaller than the US state of Montana
. Approximately 85 million people live in the larger Baltic Sea region and use the sea for various purposes 
There are nine countries with a shoreline at the Baltic Sea: Denmark
(at the Gulf of Finland, and at the Russian exclave of Kaliningrad Oblast), Lithuania
, and Sweden
Arms, Bays, Gulfs, and Spits
The Gulf of Bothnia
between Finland's west coast and Sweden's east coast is the northernmost arm of the Baltic Sea, the shallow Gulf of Finland
between Finland and Estonia is the easternmost. The Gulf of Riga is a bay between Latvia and Estonia. The Gulf of Gdańsk
, also known as Gdańsk Bay, includes the Bay of Puck
and the brackish water Vistula Lagoon
, which is separated from the Gdańsk Bay by the Vistula Spit, a peninsular sand stretch. A similar spit lies to the northeast; it is the 98 km long Curonian Spit
, a sand-dune spit between Kaliningrad Oblast and Lithuania that separates the Curonian Lagoon from the Baltic Sea.
There are about sixty rivers
drain into the Baltic Sea. The rivers and rainwater are the reasons that the water of the sea is brackish, a mixture of fresh water and saline seawater. The sea is the largest expanse of brackish water in the world.
The largest rivers are the Neva
, the navigable Russian river that connects Lake Ladoga
with the Neva Bay, the easternmost part of the Gulf of Finland. The Vistula
, Poland's largest river empties into Gdańsk Bay. The Oder
river, which in parts forms the border between Poland and Germany, flows into the Szczecin Lagoon (Oder Lagoon). The 1,020 km long Daugava
(Western Dvina) opens out into the Gulf of Riga, the Nemunas
(Memel) empties into the Curonian Lagoon, the Kemijoki
, Finland's longest river, spills into the Gulf of Bothnia at Kemi. The Narva
, Estonia's largest river connects Lake Peipus
with the Gulf of Finland. The mouth of the Swedish Lule River
(Luleälven) is at Luleå, the port city at the Gulf of Bothnia, the Torne
river forms for some length the border between Sweden and Finland; its mouth is at the northern end of the Gulf of Bothnia.
is an autonomous territory under Finnish sovereignty with a Swedish speaking population. The archipelago with more than 6,000 islands and islets at the entry of the Gulf of Bothnia in the Archipelago Sea (Finland). Other larger islands are Hailuoto
, west of the city of Oulu, and the Kvarken
Archipelago with the islands of Replot
near the city of Vaasa. Nearby is the Swedish island group of Holmöarna. Sweden's largest islands are Gotland
are Estonia's largest islands.
, the trapezoidal Danish island south of Sweden, its center is covered with one of the most extensive forests in Denmark (Almindingen). Lolland, Falster, and Møn are other Danish islands in the Baltic Sea.
The Polish Wolin
island between the Bay of Pomerania and the Oder Lagoon is home to the Wolin National Park. Wolin is separated from the German/Polish island of Usedom
by the Strait of Świna. Rügen
are Germany's largest island in the Baltic Sea. Kotlin
, the Russian island located near the head of the Gulf of Finland lies about 30 km west of St Petersburg
There are more than 200 ports in the Baltic Sea. Virtually all cities along the coast have some kind of a harbor.
The largest ports are also several national capital cities on the coast like Helsinki
, and Riga
Other important Swedish port cities are the cities of Helsingborg, Ystad, Malmö, Gothenburg, Trelleborg, Halmstad, Gävle, Sundsvall, Luleå, Norrköping, and Visby. Major Finnish ports are Turku, Kotka, Pori, and Rauma. Largest German Baltic Sea ports are Lübeck, Rostock, and Kiel
. Poland's port cities are Gdańsk, Szczecin (Stettin), and Gdynia. There are two major Russian ports, one at Kaliningrad
, the other at Saint Petersburg
. There are several ports in the Baltic countries
, Latvia has two major port cities besides Riga, Ventspils and Liepāja. Lithuania's main port is Klaipėda, and Estonia's chief ports are Tallinn and Pärnu.