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The upper Great Lakes basin is suffering a decrease in water levels, but immediate action is unnecessary, according to Canadian and U.S. experts. The causes of the drop include climate change, shifting weather patterns and earlier dredging and erosion in the St. Clair River. The bi-national, independent International Upper Great Lakes Study (IUGLS) Board states in a report that, between 1963 and 2006, the decrease in the levels – or "heads" – between Lake Huron and Lake Erie is an average of approximately 23 centimeters. Lake Michigan has also been affected because lakes Michigan and Huron act as one body of water and remain at the same level.

Global warming and lack of rain and snow account for nine to 17 centimeters of these changes, according to the report. The cause of seven to 14 centimeters of the reduction is a rise in the amount of water the St. Clair River can carry. However, since 2000, the river’s capacity has actually diminished slightly, meaning that the head has increased a bit since then. Additional reasons for the movement include adjustments in the earth’s crust as the land rebounds from the weight of glaciers in the last ice age.

Lake levels vary each day, mainly due to changing climate, wind and weather conditions. Climate is the driving force over time. For instance, increased evaporation leads to lower levels. The northern part of the Great Lakes basin, around lakes Superior and Ontario, has been very dry during the past decade; whereas the southern part of the basin, in Lake Erie, has received more average amounts of precipitation.

Water levels may also appear to rise or fall, depending on the perspectives of individuals, rather than on measured changes. Boaters who were used to relatively high levels from the 1960s to the late 1990s, and between the mid-1980s and the late 1990s, were left with perceptions that such high levels were “normal.”

The International Joint Commission (IJC) has a limited effect on water levels by using control boards to allow more or less water into different bodies of water. Questions about areas with control boards include how much water should flow through power dams, when, and how often to change the amounts. The effects of the boards vary. For instance, the dams on the St. Marys River have much smaller effects on the head of Lake Superior than the dam on the St. Lawrence River does on the flow out of Lake Ontario.

For many years, the IJC has debated whether to install gates on the St. Clair River to regulate the flow out of Lake Huron, and would like to receive comments from boaters on this issue. The public has opposed this addition in the past, and that, combined with the fact that the gates could possibly increase damage to shoreline property during high water periods, has led to inaction on the issue.

Repeated dredging of the St. Clair River has occurred since the late 1850s for commercial navigation purposes. It deepened the channel to 8.2 meters between 1960 and 1962, lowering the levels of lakes Michigan and Huron. All dredging since then has been to maintain this depth for shipping, and it has not caused any erosion or other changes in the St. Clair River since 1962.

The report, “Impacts on Upper Great Lakes Water Levels: St. Clair River,” is the first from the IUGLS. The U.S. and Canadian governments have funded the study equally, at the request of the IJC under the authority of the Boundary Waters Treaty. The IUGLS released a draft report on May 1, 2009, and altered it based on peer review, additional research and public comments, partly aquired from 17 public meetings. The final report of the study is expected early in 2012.

The IJC has posed four questions regarding the St. Clair River system that nearly 100 engineers and scientists have been working to answer since 2007, with input from independent peer reviewers and the public. They are:

Has the water-carrying capacity of the St. Clair River changed, and if so, why?

What effect could an altered flow have on water levels in the upper Great Lakes?

What other factors (such as climate) may be affecting the change in water levels?

What actions, if any, should governments take to remedy concerns about low water levels?