A collection of six maps that show areas and approximate dates and degree of ice formation. River Ice - Freeze-Up shows the average dates on which rivers are completely frozen over. River Ice - Break-Up shows the average dates on which rivers are completely free of ice. Lakes - Ice-Free Period shows the average time between clearing and first formation of ice in lakes. Sea Ice - Winter denotes open water and sea ice degree / type for Arctic, Atlantic and interior sea ice areas. Sea Ice - Summer, Heavy Ice Year and Sea Ice - Summer, Light Ice Year show ice cover in tenths which is the amount of the water surface covered by ice as a fraction of the whole area measured on a scale of ice concentration from 0/10 (no ice cover) to 10/10 (full ice cover). These last two maps also indicate the pattern and direction of iceberg drift.