Typical advance of sea ice over from late summer to late winter is shown on this map. Sea ice is any form of ice that is found at sea and has originated from the freezing of seawater. Formation of sea ice begins in mid-September in the Canadian Arctic and advances southward through the onset of winter. Sea ice begins to form in the St. Lawrence estuary around the first of January, and advances from coastal inlets into the Gulf of St. Lawrence. Sea ice in Canada normally reaches a maximum extent at the beginning of March. The map shows the typical advance of the sea ice cover from late summer (mid-September) to late winter (mid-March). The dates shown in the legend of the map indicate the extent of the sea ice cover at those dates.