The lake, which is about 18 inches below average, has dropped nearly 2.5 feet over the past decade and the entire Great Lakes Basin is seeing reduced water levels, CBS News said Friday.

Recreational boaters are moving boats to marinas set in deeper water and commercial shippers are being forced to reduce cargo loads.

A 20 percent less rain has fallen into the lake during the current drought and warmer winter temperatures mean less ice cover and more evaporation. Scientists, however, say they don't know if it is a natural pattern or global warming.

"Within a couple of years, they should be rising again," ecologist Doug Wilcox, branch chief of the U.S. Geological Survey Great Lakes Science Center, told CBS. "If they continue to go lower and lower, that would indicate to me that we're outside the bounds of the natural pattern."