Lakes Superior, Michigan-Huron and St. Clair were below their long-term average (1918-2012) water levels in August. Lakes Superior and Michigan-Huron continue their 14 consecutive year stretch of below average water levels, the longest in each of their recorded histories. The latest six month forecast does not call for record low levels on any lakes given any scenario. The most probable forecast shows Lake Michigan-Huron remaining 12 to 13 inches ABOVE record lows through February.
Expected impacts to navigation: The August monthly mean water levels of Lakes Superior and Michigan-Huron were both above chart datum, but both lakes remain below their long-term averages. Lake Superior is expected to remain above chart datum through December and be 1 to 3 inches below datum in January and February. Lake Michigan-Huron is forecasted to fall below chart datum by November. Low water levels on the Great Lakes will affect navigation in several ways. The first is that harbors and ports on Lakes Michigan, Huron and Superior will experience lake levels near low water datum during much of this navigation season. Shippers will have to continue to light load. Groundings will be much more likely and some harbors may close. Waukegan Harbor is currently closed to commercial navigation. Many recreational harbors have also been affected. Also, it is important to note that because the Great Lakes operate as a system with interdependent ports, problems in the upper lakes have negative impacts across all the commercial projects throughout the system, including the ports on Lakes Erie and Ontario. Light-loading caused by low levels on the upper lakes will have repercussions throughout the system with increased costs to shippers in the agricultural and manufacturing sectors. Every foot of lost depth requires a 1,000-footer to load 3,200 tons less. At 1.5 feet below datum, they are losing 8-10 percent of their carrying capacity. This causes significant economic impacts in increased shipping costs.