Sometimes it drained to the north IIRC from an article I read about a year ago.Mark said:Actually, shipping in the Great Lakes stops for the winter now. Usually the last ship goes by Detroit in late December and the first one of the year in March. The exact dates vary from year to year as the Coast Guard monitors conditions. Storms and ice are the reasons. In fact, ice fishing is very popular on Lake St. Clair, located between Lake Huron and Lake Erie.
There's no reason why the Great Lakes can't drain north in the future, but given that the ice sheets were retreating north, the water could only run either south or east, depedning on the exact conditions.