We are on our way from Vasa (Vaasa), Finland, to Umeå, Sweden, a 4 hour trip by Wasaline ferry. It's the northernmost year round passenger ferry. As you can see the ice is thick (30-50 cm close to the coast), but icebreakers keep the fairway open. In the second picture the colors represent different kinds of ice. Dark grey is the most solid and thick. Blue stands for open water. So the open water is only a fraction of the total travel distance. https://www.wasaline.com/en/