The U.S. Army Corps of Engineers, which tracks Great Lakes ups and downs, recorded Michigan-Huron at 576.6 feet above sea level for October. That's an inch-and-a-half above the lowest point for that month since the agency began keeping records in 1918, and about 6 inches above the all-time low recorded in March 1964.
Michigan and Huron are considered one lake from a hydrological perspective because they have the same surface level and are connected at their northern ends by the 5-mile-wide Straits of Mackinac.
All the lakes were below their long-term averages for the month and lower than a year ago because of an abnormal lack of snow last winter and the hot, dry summer, said Keith Kompoltowicz, a hydrologist with the Army Corps district office in Detroit. A wetter-than-usual October that included Superstorm Sandy has made only a slight difference.
"We would need several months and several seasons in a row" of generous rainfall and snowmelt to restore the lakes to their historical averages, Kompoltowicz said.
The storm probably raised the easternmost lakes—Erie and Ontario—and perhaps gave a slight boost to Huron and Michigan, he said. But those gains could be offset by the seasonal decline that takes place every fall and winter. Levels tend to rise in spring and summer, fed by rain and melting snow.
"There's a constant battle between how much rain and runoff is coming into the lakes versus how much is leaving through evaporation," Kompoltowicz said. "This time of year, evaporation usually wins out."
Low levels have been a recurring concern on most of the Great Lakes since a sudden drop-off in the late 1990s. They cut into cargo shippers' profits by forcing them to carry lighter loads. They cause shallow water in marinas, dry up wetlands crucial for wildlife, and cause vegetation to grow on beaches.
Local officials along the coasts are pleading for stepped-up dredging in shallow ports, but a tight budget limits what the Army Corps can do—particularly for small harbors, said David Wright, operations chief for the Detroit district.
Despite recurring conspiracy theories about secret pipelines to the West or stepped-up outflows from the Chicago River, officials say the declines have been driven almost entirely by less rain and snowfall. Additionally, milder winters have produced less ice cover, boosting evaporation.
The Army Corps is scheduled to release a six-month lake levels forecast Monday.
"If we were to see a very similar winter to what we had last year ... the potential is very real for new record lows," Kompoltowicz said.