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 Preliminary data show Superior's average water level in September dipped 1.6 inches beneath the previous low for that month reached in 1926, Cynthia Sellinger, deputy director of NOAA's Great Lakes Environmental Research Laboratory, said Sunday.
The U.S. Army Corps of Engineers, which uses a different measuring technique, calculated the September level at 4 inches below the record, said Scott Thieme, chief of hydraulics and hydrology for the Detroit district office.
It's the first time in 81 years that the biggest and deepest of the lakes has reached a new monthly low, Sellinger said. The Army Corps recorded Superior as also setting a record by a half-inch in August. But the NOAA lab had the lake at slightly above its record level then.
Either way, the lake has plummeted over the past year and has dipped beneath its long-term average level for a decade
-- the longest such period in its known history.
"I've been here since 1959 and this is the lowest I've seen it," said Joel Johnson, owner of Lakehead Boat Basin in Duluth, Minn.
Some areas had so little water last spring and summer that recreational boats couldn't reach docking slips, although other marina operators managed to operate normally.
Commercial shippers, who haul iron ore and coal across the lakes to manufacturing centers such as Detroit, have been unable to fill cargo holds to capacity for fear of scraping bottom in shallow channels.
"Light loading has been just creaming the industry this year," said Glen Nekvasil, spokesman for the Lake Carriers Association.
All the Great Lakes, which together make up about 20 percent of the world's fresh surface water, have been in decline since the late 1990s.
Lakes Huron and Michigan are about 2 feet below their long-term average levels, while Lake Superior is about 20 inches off. Lake Ontario is about 7 inches below its long-term average and Lake Erie is a few inches down.
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 The NOAA lab bases its statistics on measurements taken by a gauge near Marquette. The Army Corps averages the numbers from several gauges around the lake.
Levels typically fluctuate through the year. Superior, a feeder for the other lakes, rises in spring and summer as melted snow flows into its headwaters, then recedes in fall and winter.
But precipitation is well below normal in the Lake Superior watershed, and unusually mild winters have reduced the winter ice cap, boosting evaporation.
The region got some badly needed rain in September -- up to 5 inches in some places.
Bill Duckwall, a fishing and boating outfitter in Marquette, said the big lake seemed a bit higher lately.
"I think it's definitely coming back a little bit," he said.
But with Superior at its all-time low point for the beginning of fall -- when the lake usually begins its annual drop-off
-- prospects for quick improvement wouldn't seem good.
Scientists point to a number of possible causes for the low water, including historical cycles, weather patterns and global warming.
"Is this going to continue? That's the big question, and we don't know," Sellinger said.
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On the Net:
NOAA's Great Lakes laboratory:
http://www.glerl.noaa.gov/data/
now/wlevels/levels.html
Army Corps of Engineers: http://www.lre.usace.army.mil/
[Associated Press; by John Flesher]
Copyright 2007 The Associated Press. All rights reserved. This
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