for National Geographic News
Lake Superior, the world's largest freshwater lake, has been shrinking for years—and now it appears to be getting hotter.
Beachgoers at the lake, which is bounded by Wisconsin, Michigan, Minnesota, and Ontario, Canada, must walk up to 300 feet (100 yards) farther to reach shorelines. (See a map of the region.) Some docks are unusable because of low water, and once-submerged lake edges now grow tangles of tall wetland plants.
The remaining lake water is also heating up at dramatic rates.
Such changes are sparking implausible conspiracy theories about the water's fate, along with new scientific investigations.
Researchers are also starting to suspect that the shrinking and heating are related—and that both are spurred by rising global temperatures and a sustained local drought. (Related: "Warming May Be Drying Up Alaska's Lakes, Photo Study Says" [October 17, 2006].)
No More Rainy Days
From the late 1960s to 1999, there was a 30-year period with water levels above average, said Scott Thieme, chief of the Great Lakes Hydraulics and Hydrology Office for the U.S. Army Corps of Engineers in Detroit, Michigan. But in 1999, the upper lakes started to fall below average and have mostly stayed that way.
"Lake Superior is in its largest stretch of below average water levels since we've been recording water levels," Thieme said.
Scientists predict that by this fall, the lake will set a new record low—about an inch (2.5 centimeters) below the old one.
"Now people are saying, 'Wow, this is becoming more significant,'" Thieme said. (Related: "Shrinking African Lake Offers Lesson on Finite Resources" [April 26, 2001].)
Falling lake levels have seemed dramatic to lake residents because they've spent most of their lives alongside a swollen Lake Superior, he added.
Some locals suspect water is being secretly diverted from the lake to places such as the thirsty West. But Thieme said that theory doesn't hold water.
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