On 20 October 2023, an exceptionally violent easterly storm caused water levels to rise to historic heights. Waves crashed over harbour jetties, jetties were shattered, and yachts broke free and sank. When the water receded the following morning, scenes of unprecedented destruction were evident in numerous harbours. Regionally, it was the worst Baltic Sea storm surge since the disaster of 1872.
Why the water built up
Days before 20 October, weather models had already indicated a dangerous development over the Baltic Sea. Meteorologists warned of an unusual combination of strong easterly winds, high water levels and heavy swells.
The easterly wind, which persisted for several days, drove water into the western bays of the Baltic Sea. The distinctive geometry of the shallow western Baltic Sea and its fjords exacerbated the build-up of water. In addition, already elevated initial water levels and natural oscillations of the Baltic Sea water – known as seiches – influenced the situation.
What was exceptional about 2023 was not only the height of the water, but also its duration. According to subsequent analyses by the BSH, water levels of at least one metre above the usual level were recorded in Flensburg for more than 50 hours throughout the event. Coastal defences, harbour jetties and jetties were consequently under strain for a long period.
When the mooring lines came loose
By Friday morning, the situation was already tense. Some boat owners had managed to have their boats taken out of the water in time. However, crane appointments were in short supply, and marinas in many places were still unusually full. September had been warm, and many boat owners had extended their season.
The stern lines attached to the dolens were a particular cause for concern. During extreme high water, conventional line eyes could slip over the tops of the dolens. The vessels would then lose their hold, even though the mooring lines themselves had not snapped. The length of the lines also became a problem: when the water level rose by more than two metres, the usual reserve length of the mooring lines was sometimes insufficient.
The crucial hours came on Friday evening. Between around 6 pm and 10 pm, the situation escalated in several harbours. The water reached its highest levels, whilst the storm continued to blow with great force from the east. Wherever a boat lost its mooring, neighbouring yachts were suddenly at risk too. The first collisions led to further mooring lines being torn loose and damaged jetties. A chain reaction set in.
Schilksee, Damp and Maasholm have been badly affected
According to Sporthafen Kiel GmbH, 48 vessels sank in Schilksee alone. Others were left severely damaged, stranded on broken jetties or thrown against the shore defences. The waves had eroded the breakwater, and parts of the harbour infrastructure were destroyed.
The situation at Damp Marina on Eckernförde Bay was no less dramatic. The marina, which faces east, was hit particularly hard by the floodwaters and the heavy swell. Of the 100 or so yachts that, according to reports at the time, were still moored in the harbour, around 35 were severely damaged, sank or were washed ashore.
Maasholm, at the mouth of the Schlei, was also severely devastated. Around 20 boats sank. At the Wiking marina in Schleswig, situated well inland along the Schlei and, at first glance, better protected, almost all of the 150 or so boats moored there were affected. The following accounts describe how differently the marina operators experienced the night: People affected in our storm surge report in detail.
The storm surge also hit the Danish coast. The southern islands and the ports on the east coast were particularly badly affected. In Mommark on Als, the outer jetties, jetties and parts of the harbour infrastructure were destroyed; the harbour restaurant was badly damaged and sections of the adjacent campsite were washed away. The Consequences for Danish ports kept operators and water sports enthusiasts busy long after the stormy night.
Rescue operation amidst rubble and destroyed jetties
Subsequent estimates from the industry put the number of severely affected vessels at around 400, including some 150 sunken boats. However, different figures were circulating depending on when the survey was carried out and the method of counting used. There was no comprehensive, uniformly recorded final tally of all the damage.
The salvage of the sunken and stranded yachts turned into a major logistical operation. Salvage companies, divers, boat builders, insurers and port operators had to coordinate their efforts. In the destroyed harbour facilities, regular crane sites were often inaccessible, some jetties were no longer passable, and sunken boats were trapped beneath the rubble. Salvage vessels equipped with floating cranes had to be deployed.
For many owners, the loss was particularly bitter. Some had maintained and restored their boats over decades, whilst others had only recently invested substantial sums in repairs and equipment. Even if a boat was still recognisable from the outside after being salvaged, that by no means meant that repairing it would be economically viable.
Reconstruction takes years
For the harbour operators, too, a massive task lay ahead following the salvage operation. Entire jetties had to be replaced, dolphins re-driven into the seabed, breakwaters repaired, electricity and water pipes renewed, and harbour basins cleared of sunken debris. Just how unevenly the work was progressing was already evident from the Taking stock one year on from the storm surge clearly.
The Damp marina, in particular, turned out to be a long-term regeneration project. In the spring of 2026 YACHT reported on extensive dredging and backfilling work, whilst the marina, with around 110 berths, remained open only on a limited basis.
What boat owners have learnt from the stormy night
These events demonstrated that standard mooring techniques can reach their limits in extreme water levels, and that a supposedly sheltered berth does not offer absolute safety. At the same time, it became clear just how dangerous it can be when boat owners try to save their boats right up to the last moment. The decision to leave the boat and the jetties in good time may be more important than saving one’s possessions.
Book recommendation
Weather at sea explains how different weather patterns develop and shows where boaters can obtain reliable weather information. The book covers low- and high-pressure systems, local and regional weather events, as well as sea states and ocean currents. Clear diagrams and explanations on meteorological trip planning help readers to better understand weather developments and their significance for their next trip.
How did you experience the 2023 Baltic Sea storm surge, and what has changed at your mooring since then? Please share your thoughts in the comments.
Lars Bolle
Chief Editor Digital