Record St. Clair River Ice Jam of 1984

The record St. Clair River ice jam of April 1984 produced major impacts on the levels and flows of the Great Lakes, and on navigation throughout the system. Following the onset of the jam, Lake St. Clair water levels dropped about 0.6 m as the inflow was decreased by the jam. At the peak of the jam the flows were reduced by approximately 65%. The jam had a duration of 24 days. Following the jam breaking on April 29, 1984, the waters of Lake St. Clair rose rapidly, recovering approximately 75% of the drop in levels in four days. Computer simulations indicate that it will take about a year for most and at least 3 years for all the excess water stored in Lakes Michigan and Huron during the jam to be dissipated and for levels in those lakes (and Lakes St. Clair and Erie, downstream) to return to prejam conditions.