Video images of the bottom of the St. Clair River show no evidence of erosion that might lead to lowering water levels on Lake Huron and Lake Michigan, scientists working on a joint Canada-U.S. advisory group said Thursday.

The International Joint Commission said its findings were preliminary, however, and "more work involving sediment transport measurements and sediment models are planned to test this hypothesis."

The findings are part of the commission's mandate to investigate whether erosion from dredging caused water levels in Lakes Huron and Michigan to decline to near-record lows.

The $17.5 million study, launched in 2006, was prompted by two reports from the Georgian Bay Association, which represents about 17,000 people living on the Lake Huron bay.

The association said a potential culprit for the lower water levels was dredging done in the St. Clair River in the 1960s, when the St. Lawrence Seaway was being completed. The St. Clair River connects Lake Huron to Lake St. Clair and forms part of the international boundary separating Michigan from Ontario.

The theory is that the dredging led to accelerated erosion, causing a loss of 9.5 billion litres of water daily from Lakes Huron and Michigan.

Underwater evidence

The commission's underwater video, taken in September 2007 across a 50-kilometre stretch of the river, showed evidence that ran counter to this theory, instead finding an "armour layer" of coarse gravels, pebbles and stones ranging in size from 4 millimetres to 25 centimetres in size.

"Based on the capacity of the flow to transport sediment, the armour layer in the upper part of the St. Clair River is considered to be stable," the report said.

The video was taken by Bommanna Krishnappan, a research scientist with the National Water Research Institute Ontario.

Mary Muter, a spokeswoman for the Georgian Bay Association, said the IJC's report is unconvincing and contains errors.

Final report due in 2009

"It's premature for them to be releasing this information," said Muter, chairwoman of the group's environment committee. "They're wasting time and wasting money."

The commission is not expected to release its final report on the drop of water levels in the two Great Lakes until February 2009.

Drought and evaporation are also being investigated as potential causes of the water level drop.

Lakes Huron and Michigan are at their lowest levels since the 1960s and Lake Superior is at its lowest since 1926, according to a report from the Canadian Hydrology Service at Burlington, Ont.

The lower Great Lakes, Lake Ontario and Lake Erie, remain at or slightly above normal levels.

With files from the Associated Press