Sometimes during the winter months, a strong storm pushes water from the North Sea into the river Elbe. The water of the river cannot flow into the North Sea. The high tide will run unusually high.
But the storm surge is not unusual for a city like Hamburg, which is prepared. At the old fishmarket, preparations against high tide are routine: parked cars need to be removed, the doors of the historic auction hall are opened and water barriers are set up to protect the other buildings.