Which Great Lake is most vulnerable to winter ice cover?

Lake Erie is the Great Lake most vulnerable to winter ice cover. It is the shallowest of the five lakes, with a mean depth of only about 19 metres, so winter cold can cool the entire water column relatively quickly.

Its long east–west shape and position farther south than Lake Superior also create conditions in which large areas can freeze during severe winters. Complete or near-complete ice cover has occurred, although it is not an annual event and varies substantially with weather and climate.

Lake Superior is colder overall, but its much greater depth stores more heat and usually prevents the whole lake from freezing. This is a common point of confusion: the lake with the coldest reputation is not necessarily the one most likely to become broadly ice-covered.

Ice on Lake Erie affects shipping, evaporation, lake-effect snow, and coastal hazards. Satellite monitoring is used to track coverage because the distribution can change rapidly during winter storms and thaws.