The sea stretches from 53°N to 66°N latitude and from 10°E to 30°E
longitude. A marginal sea of the Atlantic, with limited water exchange
between the two water bodies, the Baltic Sea drains through the Danish
Straits into the Kattegat by way of the Øresund, Great Belt and Little
Belt. It includes the Gulf of Bothnia, the Bay of Bothnia, the Gulf of
Finland, the Gulf of Riga and the Bay of Gdańsk.
The "Baltic Proper" is bordered on its northern edge, at latitude 60°N, by
Åland and the Gulf of Bothnia, on its northeastern edge by the Gulf of
Finland, on its eastern edge by the Gulf of Riga, and in the west by the
Swedish part of the southern Scandinavian Peninsula.
The Baltic Sea
is connected by artificial waterways to the White Sea via the White
Sea–Baltic Canal and to the German Bight of the North Sea via the Kiel
Canal
The fauna of the Baltic Sea is a mixture of marine and freshwater species. Among marine fishes are Atlantic cod, Atlantic herring, European hake, European plaice, European flounder, shorthorn sculpin and turbot, and examples of freshwater species include European perch, northern pike, whitefish and common roach. Freshwater species may occur at outflows of rivers or streams in all coastal sections of the Baltic Sea. Otherwise, marine species dominate in most sections of the Baltic, at least as far north as Gävle, where less than one-tenth are freshwater species. Further north the pattern is inverted. In the Bothnian Bay, roughly two-thirds of the species are freshwater. In the far north of this bay, saltwater species are almost entirely absent. For example, the common starfish and shore crab, two species that are very widespread along European coasts, are both unable to cope with the significantly lower salinity. Their range limit is west of Bornholm, meaning that they are absent from the vast majority of the Baltic Sea.