Canada and the United States are launching a $17.5-million study to determine why water levels in the upper Great Lakes have declined to near-record lows.

The study by the International Joint Commission will consider a number of possible causes, from climate change to erosion caused by dredging in the St. Clair River.

Environment Minister Rona Ambrose announced $500,000 for the study last week. But officials say that is just the first instalment in what will be a major, five-year research effort.

Ambrose noted that water levels in Georgian Bay together with Lakes Huron and Michigan were as much as 45 centimetres below average this summer.

"Clearly, the health of this ecosystem has global significance," she told a news conference at Parry Sound. "Change is already upon us."

Huron and Michigan are at their lowest levels since the 1960s and Lake Superior is at its lowest since 1926, reports the Canadian Hydrology Service at Burlington, Ont.

The decline has caused problems for navigation, recreation, power generation and the ecology of the area. Wetlands are drying up, docks are stranded and beaches in some areas are overgrown with weeds.

"People that have lived along the shoreline and thought they have a million-dollar property no longer do, because instead of having a nice beach or a nice rocky shoreline in front, they've got muck with bulrushes growing in it," said Mary Muter of the Georgian Bay Association.

Citing a study by Blair Associates of Oakville, Muter said the Lake Huron-Michigan water level decreased by 2.4 cm between 2000 and 2005, which she described as a major drop.

"If you converted half a centimetre into volume of water you'd be talking millions of gallons of water."

Yet the lower lakes, Ontario and Erie, are at or slightly above normal levels, which has scientists baffled. Normally, water levels throughout the lakes would rise and fall more or less in tandem.

Computer models simulating climate change predict that water levels will decline throughout the Great Lakes, but don't explain why the upper lakes would be affected more than the others.

"The real thing that's got everybody concerned is not only are Lake Michigan and Huron dropping, but they're dropping relative to Erie," said Frank Quinn, a hydrology consultant at Tecumseh, N.Y.

"The lakes have been low in the past, but the graphs show that all of a sudden starting probably in the late 1980s or early 1990s there came a major difference in the water levels.

"If it was just generally low lake levels you would expect to find the same problem on Erie and Huron."

One possible explanation is that global warming has changed rainfall patterns, said Ralph Moulton at the Canadian Hydrology Service.

There has been unusually low rainfall this year in Northern Ontario compared with the southern part of the province, but it's not clear if that is part of a trend. 

Another possible culprit is dredging in the St. Clair River when the St. Lawrence Seaway was being completed. The theory is that the dredging led to accelerated erosion, allowing increased outflow to Lake Erie.

"By dredging they removed the hard covering core of the bottom sediments," said Muter. "Once you remove that layer you expose soft eroding clay to a very high current there."

She said there is a lot of concern about property values around Georgian Bay.