Cynthia Bowers is a CBS News correspondent based in New York.
When you first see Lake Superior from the hills above Duluth, Minnesota, the view can take your breath away. The largest of the Great Lakes sprawls like an ocean. To see that the water level is down by 18 inches or so this summer you have to get closer—and you have to know what to look for. You have to examine pilings along the many docks and look at the patterns in the sand along a stretch of beach-- or ask someone who lives or works here.
The commercial shipping fleet knows all about the water level. The giant freighters that ply Lake Superior carrying cargo containers and iron ore are lying so low in the shallow channels they've had to reduce their loads by 270 tons per 1,000 foot ship for every inch the water drops. That's 5400 pounds less cargo and that means an extra 50 or 60 trips across the 160 mile wide lake to make up the difference.
Recreational boaters are finding out the hard way the "new landscape" can be treacherous. Some boats have gotten hung up on, or near, newly exposed sandbars and some boat owners are being forced to move to deeper waters.
Although the other lakes aren't experiencing such a drastic change, scientists say the water level across the entire Great Lakes basin is down and they want to know why. A five-year, $17 million study is underway to find out how much of this is being caused by Mother Nature and how much, if any, is caused by man.
The prevailing thought has always been that man changes the lake levels by inches, nature changes it by feet. But regardless, when you consider that the Great Lakes as a whole make up one fifth of all the fresh water on earth, understanding them could be key to our survival.