Historic Baltic Sea Water Levels Drop Equivalent to Losing Two Lake Vänerns

Sweden and the Baltic region are experiencing an unprecedented environmental event as persistent high-pressure blocking and sustained easterly winds have pushed out approximately 300 cubic kilometers of water from the Baltic Sea. This amount is roughly equivalent to twice the volume of Lake Vänern, Sweden's largest lake, which contains about 160 cubic kilometers of water.

The Swedish Meteorological and Hydrological Institute (SMHI) reports that this significant outflow has occurred through the Øresund Strait and the Danish straits, including the waters of both the Gulf of Bothnia and Gulf of Finland. Despite water level increases during storm events around New Year’s—specifically storms Johannes and Anna—the prevailing conditions have led to a notable drop in Baltic Sea water levels.

This rare phenomenon, observed only a few times in the last 200 years based on long-term measurement series—Stockholm’s records alone span over two centuries—has led to visible effects along the coasts. For example, a shipwreck from the 1600s has become exposed near Kastellholmen in Stockholm. Additionally, many coastal docks have been left dry, and ferry routes have been forced to change course due to shallower waters.

The cause of this occurrence is a stagnant high-pressure system over Sweden causing prolonged cold weather combined with strong easterly winds that effectively displace water from the Baltic Sea. Finland and Swedish measuring stations have recorded historically low levels.

While this drop may create favorable conditions for an increased influx of fresh, oxygen-rich water to the Baltic Sea's oxygen-depleted seabeds, experts caution that significant challenges remain. According to hydrologist Jörgen Öberg, although reaching these low levels is a critical first step, several additional factors are necessary to restore healthier conditions. These include prolonged low-pressure, westerly wind weather patterns during autumn, and the arrival of sufficiently salty, cold water often stirred by storms, essential for oxygenating the deep sea layers. The process is uncertain and akin to a lottery, with further steps needed before the oxygenated water can reach the seabed effectively.

This extraordinary water level decline underscores the delicate balance of Baltic Sea ecosystems and highlights the ongoing challenges in preserving water quality and marine health under evolving weather patterns.