Läänemere

Läänemere, the Estonian name for the Baltic Sea, is a large brackish sea in Northern Europe. It is bordered by Denmark, Sweden, Finland, Estonia, Latvia, Lithuania, Poland and the Kaliningrad Oblast of Russia, and is connected to the North Sea via three Danish straits: Øresund, the Great Belt, and the Sound.

Hydrologically, the Baltic is a semi-enclosed sea with limited deep-water exchange with the North Sea, leading to low salinity and strong vertical stratification. The sea covers about 377,000 square kilometres, with an average depth of about 55 metres; its deepest point is Landsort Deep at roughly 459 metres.

Geographically, it comprises several sub basins, including the Gulf of Bothnia in the north, the Baltic Proper, and the Gulf of Finland and Gulf of Riga in the east. Salinity ranges from around 2–3 psu in the northern basins to roughly 7–12 psu in parts of the western Baltic.

Ecologically, the Baltic supports a mix of freshwater- and marine species, but the system is sensitive to eutrophication, pollution and invasive species. The ecosystem is affected by climate change and varying river discharge.

Humans rely on the Läänemere for shipping, fishing and tourism. It hosts major ports such as Stockholm, Helsinki, Tallinn, Riga, Gdańsk and Gdynia, and busy maritime routes. Management of the sea is coordinated through international and regional bodies, notably HELCOM (the Baltic Marine Environment Protection Commission) and EU-wide frameworks, which address water quality, biodiversity and pollution.