A combination of weather systems, which first pushed water out of the Baltic, then pushed new water from the North Sea into the Baltic Sea led to 198 km³ of salty water making its way eastwards.
Researchers from the Leibniz Institute for Baltic Sea Research in Warnemünde, Germany, are now following the progress of the oxygen-rich water, which may reach areas of the sea currently suffering from oxygen deprivation.
The Baltic Sea is known for its brackish water and for having areas on the sea floor with so little oxygen that living organisms have had a hard time surviving.
So what does this inflow of oxygen-rich salt water mean for the Baltic Sea's ecosystem?
Radio Sweden spoke with Dr. Michael Naumann from the Leibniz Institute for Baltic Sea Research in Warnemünde, who explains more and tells us what this will mean for the eco-system in the sea off of Sweden's east coast.