Navigational dredging along the St. Clair River in southwestern Ontario has contributed to a drop in water levels in the upper Great Lakes basin, but it's not an ongoing problem and doesn't require immediate action, a panel of U.S. and Canadian experts has found.

Water levels between Lake Michigan and Lake Erie have dropped an average of 23 centimetres between 1963 and 2006, according to a report by the International Upper Great Lakes Study Board.

An increase in the water-carrying capacity of the St. Clair River accounts for seven to 14 centimetres of the decline, but there's been a slight decrease in capacity since 2000, the report said.

There's been no significant erosion of the channel along the length of the St. Clair River bed since at least 2000, it also found.

Climate is the main cause of declining water levels over time, accounting for nine to 17 centimetres, the report said. Shifts in the earth's crust as it adjusts to the retreat of glaciers are also responsible.

The report provides "greater insight" into how the St. Clair River — through which water from Lake Huron flows to Lake Erie — affects water levels in the Great Lakes, said Sujata Raisinghani, an Environment Canada spokesperson.

"The study and its report will provide Canada and the United States with the sound scientific basis needed to manage this resource into the future," Raisinghani said in an email. "Water management is a shared responsibility and we will work with international, provincial and municipal governments, and local stakeholders to ensure we are meeting the needs of Canadians."

Findings contradict earlier report

The report's findings appear to put the panel at odds with Georgian Bay Forever, a Canadian group that contends that dredging of the St. Clair River during the 1960s has increased water flow from Lake Huron to Lake Erie, causing water levels to drop.

Georgian Bay Forever argues that dredging, riverbed mining and shoreline alteration along the river near Port Huron, Mich., and Sarnia, Ont., have affected the flow of the Great Lakes and are draining water into the Atlantic Ocean.

The group, which released the findings of an independent study on the leakage two years ago, has called on the American and Canadian governments to patch up the "drain hole" that's hemorrhaging an estimated 45 million litres of water a day.

The panel's report concluded that "remedial measures to address changes in the St. Clair River since the navigational dredging in 1962 are not warranted at this time."

Climate change a concern

But measures to mitigate future changes that could adversely affect water levels need to be examined as part of a comprehensive assessment of the future effects of climate change on water supplies in the upper Great Lakes basin, it said.

The St. Clair River has been dredged periodically over the last 150 years, mostly to support commercial navigation on the Great Lakes. According to the report, the last major dredging in the river occurred between 1960 and 1962, when the navigation channel was deepened to 8.2 metres. Since then, all dredging work has been related to maintaining the channel bottom to its authorized depths.

Both groups agree that lake levels have dropped, they just have different opinions about how much they've declined, said David Sweetnam, executive director of Georgian Bay Forever.

The group wouldn't back down from its push for government action, warning that water levels could drop further.

'It would seem prudent for somebody to step up and say, "Yes, we need to take a look at this." '—David Sweetnam, Georgian Bay Forever

While the effects of climate change are still uncertain, studies have predicted that the amount of water available to replenish the Great Lakes will diminish over time, potentially resulting in a one- to two-metre drop in water levels, Sweetnam said.

"We think it's prudent now to take action to begin the process of examining what type of remedial measures should be put in place to allow us to compensate for climate change," he said.

"Given that Copenhagen is kind of drawing a lot of focus to climate change and the impact of climate change now or the causes of it, it would seem prudent for somebody to step up and take action and say, 'Yes, we need to take a look at this.' "

The panel was appointed by the International Joint Commission, which advises the U.S. and Canadian governments on matters affecting the Great Lakes.

The panel will present its findings to the commissioners, who are expected to hold public hearings in March, Sweetnam said. The group will try to make its arguments for action at the hearings.

Raisinghani noted that Lakes Michigan, Huron, St. Clair and Erie are experiencing higher water levels because of higher-than-average water supplies resulting from rain and melted snow, as well as lower evaporation rates and cooler temperatures.