Lakes Huron and Michigan are not losing extra billions of gallons of water daily because of navigational dredging as a Canadian group contends, a scientific panel said Tuesday.
After a two-year, $3.5 million study, the U.S.-Canadian panel concluded there was no reason to stem the flow from Lake Huron by placing structures in a river that connects Huron with Lake Erie to the south.
The report disagreed with Georgian Bay Forever, a Canadian environmental charity that has commissioned engineering studies of the St. Clair River. Those studies found that human activities, primarily dredging during the early 1960s, enlarged the river bottom and increased the volume of water moving down the river from Lake Huron to Lake Erie.
Because of that, the group says, Lake Huron is losing up to 12 billion gallons per day in addition to its normal outflow _ enough to fill 10,000 Olympic-sized swimming pools.
The excessive loss is causing artificially low levels in Lakes Huron and Michigan, Georgian Bay Forever says. Geologists consider those lakes a single water body because they converge and have the same surface levels.
Low water has been a contentious issue for a decade on both lakes, causing millions in losses for shippers, marina owners and other businesses, although levels have edged upward the past couple of years and are near their historical averages.
The government report said several factors _ especially precipitation and evaporation _ have influenced differences in levels since the early 1960s.
It contradicted the Canadian group's belief that losses through the St. Clair River are a leading cause of the slump on Michigan and Huron. The river's average flow jumped by 3 to 5 percent during the mid-1980s, possibly because of ice jams or maintenance dredging. But the flow dropped within a few years and today is less than 1 percent above the normal rate, it said.
The river bed changed slightly between 1971 and 2000 but has not eroded significantly since then, said the report by more than 100 scientists and engineers. It was requested by the International Joint Commission, which advises both nations on Great Lakes matters.
"The main conclusion is that there's not a drain hole in the Great Lakes," said John Nevin, spokesman for the study panel. "It's more of a small drip that really isn't significant enough to merit action to stop at this time."
Still, the panel recommended the U.S. and Canadian governments consider whether climate change might affect water levels enough to justify regulating outflows from Lake Huron in the future.
Mary Muter, a member of Georgian Bay Forever's board, said the panel's findings were based on inaccurate depth measurements and other errors.
"They created ... data for a hypothetical river, not the St. Clair River," Muter said. "We have serious concerns about how they have done their work."
The group will continue pushing both nations to take action, she said.
Study leaders defended their methods in a phone conference with reporters, saying their analysis was more extensive than the Georgian Bay group's. It also underwent peer review, which led to some changes after a preliminary version was released in May.
Ted Yuzyk, Canadian co-chairman of the study group, dismissed the Georgian Bay Forever water loss claims. "Those are numbers that are made up," he said. "They're not credible."