Lake Superior has plunged to a record low for the month of August, this week surpassing the previous August low-water mark set in 1926.

After a long decline that has mirrored the Northland's worst drought in half a century, the mean level of the lake dropped to 600.4 feet above sea level, surpassing the previous August low mark of 600.5, said Carl Woodruff, hydraulic engineer for the U.S. Army Corps of Engineers Detroit District.

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It's the first record set during the lake's current downturn.

The lake probably will stay in or near record-low territory through autumn and into winter. But it remains uncertain if the lake's cyclical water level will remain low enough by spring to set the all-time low-water mark.

The lake hit a low of 599.97 feet in April this year, just 6 inches or so from the all-time record of 599.41 in 1926, said Cynthia Sellinger, deputy director of the Great Lakes Environmental Research Laboratory. Accurate records go back to about 1860.

"It all depends on precipitation, especially winter snow,'' Woodruff said.

The lake level rises every year from May through October and then declines into April as precipitation remains locked in snow. Low-water marks almost always are set in April before the lake begins to rise from the runoff of spring snow melt and spring rains.

A new record low for late summer and early fall wasn't unexpected. Much of the lake's watershed is locked in a severe drought. Duluth, for example, is a foot short of normal precipitation since June 1, 2006, and has received less than a quarter-inch of rain in August.

The lake is nearly 22 inches below its long-term average for August and about 10 inches below the level at this time last year, Woodruff said.

The most significant impact of the low water so far has been on shipping, with some harbors and channels now too shallow to handle Great Lakes freighters carrying full loads. That has cost industry more for transportation, with boats moving at less-than-full capacity.

The low water has made for wider beaches and less erosion, but also has left some boat landings high and dry and has caused a major drop in coastal wetland water levels -- so steep in some areas that wild rice has deteriorated.

Low water levels are not expected to affect Lake Superior's marine life, but the ongoing drought is affecting the ability of fish to enter the lake's tributaries, some of which are nearly dry.