MILWAUKEE -- Placing water retention structures in the St. Clair River may not be enough to counteract the effects of a warming climate and raise Lakes Huron and Michigan to their normal levels, experts said Monday.

As water surface temperatures and evaporation rates continue to rise, low water is likely to be a long-term problem despite significant improvement this year following heavy snows in winter and a rainy spring, according to testimony during the annual meeting of the Great Lakes Commission.

"Water levels go up and down," said Scudder Mackey, coastal management chief with the Ohio Department of Natural Resources. "It's a natural process, something that we have to learn to live with."

Levels have been mostly below normal on all five Great Lakes since the late 1990s, but the drop-off has been most severe on Huron and Michigan, which scientists consider one lake because they are connected.

Huron-Michigan has jumped 20 inches since January, exceeding its usual seasonal rise, said Keith Kompoltowicz, a meteorologist with the Detroit office of the U.S. Army Corps of Engineers. Still, it remains 17 inches below its long-term average. Lake Superior is also slightly below its long-term average, while Lakes Erie and Ontario have exceeded theirs.

Groups representing shoreline interests in Lake Huron, particularly in sprawling Georgian Bay, say climate isn't the only reason water there is extraordinarily low. They blame dredging, gravel mining and other activities that eroded the floor of the St. Clair River on Huron's southern end, accelerating the flow toward Lake Erie.

Studies have shown those actions caused Huron and Michigan to fall 10 to 16 inches. Some groups put the loss at 20 inches.

In April, the International Joint Commission -- which advises the U.S. and Canada about the Great Lakes and other shared waters -- recommended a study of installing structures resembling underwater speed bumps in the St. Clair that could raise Huron and Michigan by 5 to 10 inches. Neither federal government has acted on the proposal.

A panel discussion before the Great Lakes commission, which represents states and Canadian provinces in the region, revealed skepticism about the idea.

"Lows on Lakes Michigan and Huron may remain if we have increased evaporation and less precipitation, even if we put in compensating structures," said Mackey, who participated in the International Joint Commission study.

It could take up to 25 years to plan, design and build the structures and another decade for them to boost levels as much as hoped, said Deborah Lee, regional business director for the Army corps. In the meantime, they could rise or fall on their own.

"We can't predict what the effects of climate will be with the accuracy to make these kinds of decisions," Lee said.

Roger Gauthier, chairman of a group called Restore Our Water International, which favours regulating the lake levels, said structures could be installed much faster than Lee predicted. Once in, they could boost Huron-Michigan 60 per cent within three years, he said.

"We need to ... be able to act in a time frame that treats this like a crisis," he said.

Trying to regulate Huron-Michigan would require a difficult balancing act among competing interests, said Daniel Injerd of the Illinois Department of Natural Resources.

Gauthier countered that all would benefit from more stable and reliable levels.