Local ports could run into problems if water levels in Lake Michigan keep going down. The U.S. Army Corps of Engineers reports the lake is 28 inches below the long term average – and still falling.

For each inch the lake decreases, cargo ships are forced to lighten their loads. The tonnage left behind ranges between 50 and 300 tons per inch, depending on the type of freight.

“Hopefully we’ll see them rise before they go down much lower. Each drop is a concern to everyone in the industry,” said Tony Ianello, Executive Director of the Illinois Port District. He said lake levels are always fluctuating, but even normal fluctuations affect shipping costs. Ianello said suppliers pay in extra trips to amount to the same total shipping numbers; down the chain, the price tag could hit consumers. Most shipping in and out of Chicago’s ports is for commodities like grains, many of which are directly linked to the cost of food.

Precipitation in the Michigan-Huron region in November was nearly 70 percent below the monthly average, and the Army Corps projects Lake Michigan could fall to record lows in the coming months.

“Long term loss of water levels is no good for coastal habitats, but it’s also no good for people who like to recreate, swim, and use our Great Lakes shorelines,” said Joel Brammeier, President of the Alliance for the Great Lakes. But Brammeier said no one knows for sure whether the lakes are undergoing a long term loss, or a fluctuation.

A 2009 study of the loss of water in the Great Lakes links the long term decline to human manipulation of the St. Clair River, and to changes in climatic factors including temperature and precipitation. The St. Clair River, which connects Lake Huron with Lake St. Clair near Detroit, has been dredged periodically since the mid-1800s; some researchers say this accounts for over a foot of permanent loss in Lakes Michigan and Huron.

The two lakes hit their record low in 1964, and peaked again in 1986. Even following 2012’s scorching summer, the lake hasn’t gone below1964 levels. But the Army Corps projects that by December 30, the water will go down another three inches.

Meanwhile, the Mississippi River could be facing a complete shutdown of cargo shipping through the passage between St. Louis and Cairo, Illinois. Last week the Army Corps’ Missouri River Basin division began limiting the flow of water through a dam in South Dakota in order to preserve water in that northern region; the Missouri is a key tributary to the Mississippi at St. Louis. Because water levels were already low, the reduced input means 180 miles of the Mississippi could become impassable for barges by mid-December. Immediate solutions to the impending crisis for the river shipping industry are not clear.

The short-term solution for Lake Michigan is precipitation. If the region has another warm, dry winter, the great lake could keep disappearing before our eyes.