The water on Lake Superior is so low that he couldn't put his docks in the water this year. Where he used to see water, he now sees sandbars.

Lake Superior, the world's largest freshwater lake, has dropped to its lowest level in 81 years. The water is 20 inches below average and a foot lower than just a year ago.

The dropping levels have had serious environmental and economic consequences. Wetlands have dried up. Power plants run at half capacity. Cargo ships carry partial loads. Boaters struggle to find a place to dock.

The changes can be seen all along the 2,800-mile shore of Lake Superior, the coldest and deepest of the Great Lakes. The water has receded, sometimes 50 feet or more, from its normal shoreline.

Lake Huron and Lake Michigan are at low levels, as well, although not quite as extreme.

 Source : USA Today / Enviroment Watch

Researchers at the University of Minnesota and elsewhere study whether Lake Superior's low water levels are a result of global warming. The average water temperature of Lake Superior has risen 4.5 degrees Fahrenheit since 1979.

A drought and warm weather are the immediate cause of the drop in water levels. In the past year, precipitation was 6 inches less than the average of 31 inches. The lake's southern shore had a green Christmas in 2006. The ice and snow pack that usually cover the lake arrived late, allowing water to evaporate.

"It's been a long time since we've been this low, but it has happened," says Tim Calappi, a hydraulic engineer for the Army Corps of Engineers, which tracks water levels. "We still think this is within the range of what's normal, but we have to wait and see."

Superior isn't the only prominent North American lake or reservoir at a severely low level. Lake Mead near Las Vegas and Lake Powell on the Utah-Arizona border are about half full. Florida's Lake Okeechobee recently set a record low.

Many people living near Lake Superior don't buy drought or warm weather as the reasons for dropping water levels — a conspiracy theory is more popular. They say Lake Superior was drained through the St. Mary's River to raise the levels of Lake Huron and Lake Michigan.

"It's like the tide went out and didn't come back," says Dan Alexander, a commercial fisherman in Baraga. "We know what it is. They drained the lake." The water is so low he had to find a new place to dock his 38-foot boat.

Calappi says it's a myth that the Army Corps drains Lake Superior to help other lakes with presumably more powerful benefactors. He says the amount of water that flows out of Lake Superior is established by an international agreement with Canada. The water flow is regulated by how much water is permitted to pass through hydroelectric plants on the St. Mary's River, which connects Lake Superior and Lake Huron and, indirectly, Lake Michigan.

The Edison Sault Electric power plant in Sault Ste. Marie, Mich., will operate at less than 50% capacity this year because its water flows have been slashed as a result of the low lake levels, the company said. That pushed the company to buy high-cost power elsewhere and increase rates.

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