In winter, when the temperature drops to below minus 15°C for several days, the sea-level temperature also falls below freezing point. The surrounding docks restrict the flow of seawater, allowing ice crystals to form slowly. As a result of the prolonged low temperature, the crystals become large blocks of ice. Changes in temperature and tides crack the ice blocks and sea water washes them into small pieces of floating ice. This is the reason for the formation of sea ice in the photo.