Baltic Sea Ice: History, Pattern, and Impact on Port Operations
According to scientific research, the Baltic Sea has frozen many times. The earliest records of freezing date back to the Vikings, who traveled on the frozen sea. In the Middle Ages, freezing the Baltic Sea was a common phenomenon, significantly affecting trade and communication between the Baltic states.
In the 16th and 17th centuries, the Baltic Sea peaked at freezing. It was common for the ice to cover the entire sea. The ice, which created a solid surface, made it possible to travel on foot, in carts, and even on horseback. This unusual phenomenon attracted the attention of locals and travelers from other parts of Europe.
The freezing of the Baltic Sea has been recorded several times in recent decades, with the most notable events occurring in 1987, 1996, 2010, and 2026.
How and where ice forms
Ice formation in the Baltic Sea begins along the coasts of the northern Gulf of Bothnia and the inner Gulf of Finland, usually in late October and early November. Ice then spreads to the Quark, the open Gulf of Bothnia, and the coasts of the Bothnian Sea. In normal winters, ice also covers the rest of the Bothnian Sea, the Archipelago Sea, the entire Gulf of Finland, and part of the northern Baltic Proper.
During mild winters, the Bothnian Sea does not freeze at all and the Gulf of Finland is only partially covered by ice. In harsh winters, the ice reaches the Gulf of Denmark and the central part of the Baltic Proper. The last frozen area is north-east of Bornholm in the southern Baltic Sea.
The melting season begins in April and progresses from south to north. By early May, ice remains only in the northern Gulf of Bothnia.
The winter of 2025–2026
The 2025–2026 winter sharply broke the pattern of recent mild seasons. The icebreaking season opened in late November 2025, with the first navigation restrictions coming into force in the Bay of Bothnia. By early January 2026, Baltic ice coverage had surpassed both the previous season’s extent and the 2007–2022 median for the same date. By early February, ice covered around 144,000 km² — roughly 34% of the Baltic’s total surface.
The Polish ports of Gdansk, Gdynia, Swinoujscie, and Szczecin are “ice-free.” Even when ice forms on the surface, it is never thick enough to paralyze port operations. The 2025–2026 winter tested this resilience and icebreakers/tugs had to be used to clear channels and port basins
Please visit below links:
Polish coastline icing report (most recent published)
https://baltyk.imgw.pl//ftp/zlodzenie/wybrzeze.pdf
https://baltyk.imgw.pl//ftp/zlodzenie/mapa.pdf
Baltic Icebreaking Management: