An icy winter is part of the annual cycle on Ruissalo as well

The winter cold drops the surface temperature of sea water to close to zero. The freezing of the sea starts from the sheltered bays of the inner archipelago, and in the event of a calm cold spell, the sea is soon covered in a smooth and transparent layer of ice. During an average winter, the shores of Airisto gain a permanent layer of ice in mid-January, which remains in place until late March or early April. In other words, during an average winter the sea is frozen over for 90 days, although in mild winters this “mini-ice age” may be considerably shorter. With climate change, icy winters are only becoming rarer and rarer.