Mackinac Island sits in Lake Huron at the eastern end of the Straits of Mackinac. To get to and from the island, Michigan's tourists and residents must cross the water using a water vessel. During the winter, boats and ferries are incapable of crossing the ice, leaving residents isolated. The Straits of Mackinac freeze and ice forms what has become known as an "ice bridge." For hundreds of years, people have used this ice bridge to move between Mackinac Island and the city of St. Ignace on the mainland, but the crossing can be very dangerous. Years ago, two young girls walking across the ice bridge from St. Ignace to their home on Mackinac Island were caught in an unexpected blizzard. The girls lost their way and perished. Heartbroken by this event, the people of St. Ignace and Mackinac Island began marking out a safe path across the ice using their Christmas trees. The trees were dropped off at Doud's Market in St. Ignace and later secured in the ice, thus guiding the way from one point to another. The ice bridge is still used today by snowmobilers and cross-country skiers.