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Dry summer helps push Lake Michigan water levels to near-record lows

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Lakes Michigan and Huron, which hold about 2 quadrillion gallons of water, are mostly fed by precipitation and runoff. About 29 percent flows in from Lake Superior. On the flip side, about two-thirds of that water runs out to Lake Erie while about one third is lost to evaporation. Chicago, meanwhile, diverts about one percent of the water from Lake Michigan for its own uses.

That complex balance has led to large and hard to predict fluctuations in water levels.

Since modern records began in 1918, Lakes Michigan and Huron, which are considered one body of water connected by the Straits of Mackinac, reached an all-time low of 576.05 feet in March 1964 and an all-time high of 582.35 feet in October 1986, representing a sizable range of about 6 feet.

Though the lakes tend to follow yearly cycles, swelling in the spring and summer and shrinking in the fall and winter, sudden changes in weather can upend expectations.

Or, as Alliance for the Great Lakes President Joel Brammeier put it: “Knowing what to expect when it comes to lake levels is a really tricky business.”

That inherent uncertainty keeps the lake level forecasts from the U.S. Army Corps of Engineers to a six-month maximum.

Although one daily mean water level this month reached the record low for October, the Corps predicts that the overall monthly average will ultimately be about one inch above the record low.

After October, however, the forecast gets more dire, according to Keith Kompoltowicz, chief of watershed hydrology for the agency’s Detroit district.

“The very abnormal weather that we have seen across the Great Lakes going back to last winter has really put us in the position to possibly set new record lows,” Kompoltowicz said.

Jim Clark, general manager at the Chicago Yacht Club, said he’s not surprised, given the issues he has had to deal with this season.

In July, during the club’s Race to Mackinac, the water was so shallow in Lake Huron that all the boats couldn’t fit into the Mackinac Island municipal marina as they normally do, Clark said. During another event in September, the club also had to have the Chicago Park District clear debris from the western side of the docks to prevent boats from running aground.

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