Why the Baltic Sea Is Less Salty Than Most Oceans

Baltic Sea Salinity Facts

The Baltic Sea is the world's largest brackish water body, with salinity ranging from 0.5% to 15% (average ~8%), far lower than the global ocean average of ~35%.

Reasons for Low Salinity

• Massive Freshwater Input: Major rivers (Oder, Vistula, Neva, Daugava) discharge large volumes of freshwater.
• Restricted Exchange: Narrow, shallow straits (Kattegat, Skagerrak) limit saltwater inflow from the North Sea.
• High Evaporation vs. Ice: Evaporation increases salinity, but winter ice formation traps salt; spring melt dilutes it again.

These factors create a unique brackish ecosystem.