There is only a little salt in the waters of the Baltic Sea
The seawater of the Baltic Sea is classed as low-salinity brackish water. In the surface layers of the Baltic Sea, the average salinity is only seven grams per kilogram of water. By contrast, in the oceans, it is 35 grams per kilogram.
In the Finnish marine area, the salinity of the surface water layers varies by region. It is highest in the southern Archipelago Sea and lowest in the most northern reaches of the Bay of Bothnia, as well as the easternmost parts of the Gulf of Finland.
The salinity has decreased since the 1990s, especially in the Bay of Bothnia, but also to a lesser extent in the Bothnian Sea. Also, compared to the 1970s and 1980s, surface salinities in the northern Baltic Sea have decreased in recent decades.
Check out the long-term trends or vertical depth fluctuations in the salinity of the Baltic Sea!