The Great Lakes are part of the global hydrologic system. Prevailing westerly winds continuously carry moisture into the basin in air masses from other parts of the continent. At the same time, the basin loses moisture in departing air masses by
evaporation and transpiration, and through the outflow of the St. Lawrence River. Over time, the quantity lost equals what is gained, but lake levels can vary substantially over short-term, seasonal and long-term periods.
Day-to-day changes are caused by winds that push water on shore. This is called 'wind set-up' and is usually associated with a major lake storm, which may last for hours or days. Another extreme form of oscillation, known as a 'seiche', occurs with rapid changes in winds and barometric pressure. During storms, high winds and rapid changes in barometric pressure cause severe wave conditions at shorelines.
    Annual or seasonal variations in water levels are based mainly on changes in precipitation and runoff to the Great Lakes. Generally, the lowest levels occur in winter when much of the precipitation is locked up in ice and snow on land, and dry winter air masses pass over the lakes enhancing evaporation. Levels are highest in summer after the spring thaw when runoff increases.
    The irregular long-term cycles correspond to long-term trends in precipitation and temperature, the causes of which have yet to be adequately explained. Highest levels occur during periods of abundant precipitation and lower temperatures that decrease evaporation. During periods of high lake levels, storms cause considerable flooding and shoreline erosion, which often result in property damage. Much of the damage is attributable to intensive shore development, which alters protective dunes and wetlands, removes stabilizing vegetation, and generally reduces the ability of the shoreline to withstand the damaging effects of wind and waves.
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The level of the water in the five Great Lakes has a tremendous impact on the users of those water bodies.  Low lake levels causes problems with harbors (the water is too shallow for many boats) and the rivers that drain into them.  High lake levels cause bank and bluff erosion.  The chart below shows the periods of high and low lake levels during the past 130+ years. 

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The Great Lakes' Hydology web page provides up-to-date information on lake levels.

What factors affect lake levels?  Hydrologically, lake levels can be viewed as being a function of several factors:

LL=gains (P+R+I+Di) minus losses (ET+O+GW+Do)

LL = lake level
P = precip directly onto lakes (about 30-32 inches)
R = runon from land
I = inflows from rivers
Di = diversions of water into the lakes
(I is largely a function of land use within the basin and intensity of precipitation that falls on the basin)
ET = evapotranspiration from lakes
ET = f (summer temps, winter ice cover, winter temps, winds in all seasons, sunshine, etc.)
O = outflows in rivers at lake outlets
GW = losses to groundwater
D = diversions for municipalities and other consumptive uses, out of the lakes
D = f(dredging outlets such as the St. Clair River, diversions for drinking water and hydro power,
    regulating structures like dams and locks)

The International Joint Commission, the binational agency established under the Boundary Waters Treaty of 1909 between Canada and the U.S., has the responsibility for regulation of flows on the St. Marys and the St. Lawrence Rivers. These
channels have been altered by enlargement and placement of control works associated with deep-draft shipping. Agreements between the U.S. and Canada govern the flow through the control works on these connecting channels.
    The water from Lake Michigan flows to Lake Huron through the Straits of Mackinac. These straits are deep and wide, resulting in Lakes Michigan and Huron standing at the same elevation. There are no artificial controls on the St. Clair and Detroit Rivers that could change the flow from the Michigan-Huron Lakes system into Lake Erie. The outflow of Lake Erie via the Niagara River is also uncontrolled, except for some diversion of water through the Welland Canal. A large percentage of the Niagara River flow is diverted through hydroelectric power plants at Niagara Falls, but this diversion has no effect on lake levels.
    The responsibilities of the International Joint Commission (IJC) for levels and flows of the Great Lakes are separate from its responsibilities for water quality. Water quality objectives are set by the Great Lakes Water Quality Agreement, but decisions about levels and flows are made to comply with the terms of the l909 Boundary Waters Treaty.
    Only limited controls of levels and flows are possible and only for Lake Superior and Lake Ontario. The flows are controlled by locks and dams on the St. Marys River and in the St. Lawrence. Special boards of experts advise the IJC about meeting the terms of the treaty. Members of the binational control boards are equally divided between government agencies in both countries. Until l973, the IJC managed levels and flows for navigation and hydropower production purposes. Since then, the IJC has tried to balance these interests with prevention of shore erosion. 
    The IJC has carried out several special studies on levels issues in response to references, or requests, from the governments. In l964, when water levels were very low, the governments asked the IJC whether it would be feasible to maintain the waters of all the Great Lakes, including Michigan and Huron, at a more constant level. After a 9-year study, in l973, when water levels were very high, the IJC advised the governments that the high costs of an engineering system for further regulation of Michigan and Huron could not be justified by the benefits. The same conclusion was reached for further regulation of Lake Erie in l983.
    Two human activities, diversion and consumptive use, have potential for affecting lake levels, although they have had relatively little impact to date. Diversion refers to transfer of water from one watershed to another. Consumptive use refers to water that is withdrawn for use and not returned. Most consumptive use in the Great Lakes is caused by evaporation from power plant cooling systems.
    At present, water is diverted into the Great Lakes system from the Hudson Bay watershed through Long Lac and Lake Ogoki, and diverted out of the Great Lakes and into the Mississippi watershed at Chicago. These diversions are almost equally balanced and have had little long-term effect on levels of the lakes.
    In l982, the IJC reported on a study of the effects of existing diversions into and out of the Great Lakes system and on consumptive uses. Until this study, consumptive use had not been considered significant for the Great Lakes because the
volume of water in the system is so large. The study concluded that climate and weather changes affect levels of the lakes far more than existing human-made diversions. However, the report concluded that if consumptive uses of water continue to
increase at historical rates, outflows through the St. Lawrence River could be reduced by as much as 8 percent by around the year 2030.    
    Lake levels vary from year to year and can be expected to continue to do so. "We need to accept that we can't control the Great Lakes like we would a little inland lake," said Dr. Michael J. Donahue, director of the Great Lakes Commission, in Ann Arbor. 
    Following the period of high lake levels in the 1980s, the IJC conducted another study of levels and the feasibility of modifying them through various means. In 1993, the study concluded that the costs of major engineering works to further regulate the levels and flows of the Great Lakes and St. Lawrence River would exceed the benefits provided and would have negative environmental impacts. Instead, it recommended comprehensive and coordinated land-use and shoreline management programs throughout the basin that would help reduce vulnerability to flood and erosion damages.

Why do lake levels vary so much?
Theories for lake cycles abound.  Scientists agree, however, that strong evidence shows a yearly high-to-low cycle, and a second, larger cycle with deeper peaks and depths that occurs roughly every 30 years.  A third and more tentative theory points to extremely deep lows arriving every 150 years.
    As a rule, lakes swell to their highest in summer, as spring melting rolls down the system. Levels sink to their lowest in winter, when snow piles up and freezes flows from tributaries. This tends to be a reliable annual pattern.  But there are broader patterns of lake declines that seem to take place about every 30 years.   When historic lows were set on Lakes Michigan and Huron in 1964, the word drought was used freely by journalists and scientists.  That year, residents near Lake Charlevoix were treated to a scene from Michigan's logging past.  Axes, sawmill tools and millions of feet of sunken boards from the mid-1800s came to light from the lake's drying bed.  Similar severe lows for Lakes Erie and Ontario came in 1934, three decades before 1964.
    In the search for an even longer-term pattern, one theory poses that extended lows occur every 150 years.  Indiana geologists studying Lake Michigan sand dunes are digging into beach ridges, checking the ages of ridge sediments and charting periods of lake lows and highs.  They discovered that Michigan's waters have fallen more than 12 feet in the past 4,500 years. Other studies of Lake Superior's ridges are under way. Early results show Lake Michigan may fluctuate by as much as 4 feet during the 150-year swings.

What to do?
   One planning strategy for dealing with variations in lake levels is relocation of cottages and buildings at risk from unstable shores, an idea that outrages many lakeside property-rights groups. "We are not the problem. We are a persecuted political minority living in two countries, in a zone 300 feet wide and thousands of miles long," declared Bill Andresen, a South Haven engineer with beachfront property on Lake Michigan. Andresen is president of the International Great Lakes Coalition, a group of shoreline owners mostly from Michigan. "Our assets are on the line," he said. "Lake levels have been kept artificially high for the past three decades to please the interests of the utilities and commercial shipping."
    The coalition, which includes lawyers and civil engineers, has hatched a solution of its own.  It is petitioning (as of 2000) Canadian and American officials to build a $50-million water retainment wall between Lake Erie and Lake Ontario, on the Black Rock Canal along the Niagara River near Buffalo, N.Y. The structure would allow closer control of lake waters, more consistent flow to hydropower generators and keep Lakes Huron and Michigan at predictable levels for residents, they argue. But the Canadian-American body with the power to approve the plan has politely declined.
    Members of the International Joint Commission, in charge of all boundary waters between the two nations, have studied and rejected more than 150 bids to mechanically control the lakes.
    As they are, the lakes are regulated at only two points: Sault Ste. Marie on Superior and at Massena, N.Y., on Lake Ontario. Commission engineers rejected the plans because they concluded economic and environmental effects from new controls would be unequal on each lake. "Regulation is no longer the answer," agreed Mark Wyckoff of a private consulting firm in Lansing. He advocates construction setbacks from shore, movable structures and disclosure laws in handling property-rights claims. "We're dealing with Mother Nature in a lake system that is just so huge in scale," he said. "You don't try to change that, you adapt. Let the shoreline buyer beware."
    Past lake extremes have prompted still other solutions. During record lake lows in 1964, Sen. Philip Hart of Michigan asked Canadian officials to consider sluicing water from their distant rivers into the Great Lakes system. He reasoned that "unused" water in Hudson Bay could be better employed. The Canadians curtly refused. Scientists stress that diversions from Canada and similar plans tend to be crude and expensive. They rarely account for variations in rain and snowfall in the Ontario watershed, lake evaporation or for warming patterns seen in weather worldwide. Environmental groups object on another front, arguing that water diversions to or from the lakes only trade problems between regions. Diversions also create expectations among residents impossible to sustain over time, they say.

Another perspective...

   Each and every day, customers of the Detroit water system throughout Wayne, Oakland, Macomb, St.Clair, Lapeer, Genesee, Washtenaw and Monroe Counties consume an average of 675 million gallons of water. That’s a lot of water. Yet consider for a moment what a recent report prepared by one of the top coastal engineering firms in North America theorizes: that 845 million gallons of water is being lost every day because erosion in the St. Clair River has allowed water to flow more quickly out of Lakes Michigan and Huron. This study and others also show a permanent drop of as much as 12 inches in the long-term average levels of those lakes. When lake levels are low, this loss of water can have devastating and costly consequences for homeowners and boaters, as well as for fish and wildlife that depend on coastal habitat for spawning or nesting grounds.
   The study points to massive dredging in the St. Clair River during the early 1960s to open the upper lakes to shipping, which has been a huge economic impetus for our state and our region. The study theorizes that subsequent dredging and erosion have had the effect of pulling the plug out of a bathtub, dramatically speeding up the flow of water that eventually runs through the St. Lawrence Seaway and out into the Atlantic Ocean. Engineers who completed the study believe that removing the hardened top layer of the river bottom exposed softer material that was easily washed away by the increased flow and has resulted in nearly doubling the depth of the channel, for example, just south of the Bluewater Bridge. The U.S. Army Corps of Engineers, while acknowledging a change in the river flows, believes other factors may be the reason. Obvious factors come from Mother Nature, when she gives us more or less rainfall and snowfalls. Or it could be the way Michigan has rebounded (isostatic rebound) from the weight of the glaciers, when they left some 10,000 years ago. Another factor might be a reduction in sand supply to the St. Clair River caused by shoreline protection measures built along the shores of Lake Huron and harbor construction near the mouth of the river.
   The Great Lakes comprise fully one-fifth of the freshwater supply to the entire planet. Michigan, the Great Lakes State, looks to the lakes for its economic well-being, its quality of life and its very identity. Even at today’s prices, a gallon of oil is far cheaper than a gallon of bottled water; and although we could live without oil, life cannot be sustained without water. We shake our fists at one who threatens water diversion, and yet the amount of water being diverted, according to this study, is more than any suggested plan of diversion that another part of the country could even contemplate.

The article above was written by Candice Miller, Published in the Lansing State Journal, April, 2005 (and slightly edited here)


Parts of the text on this page have been modified from the NOAA Publication, "The Great Lakes An Environmental Atlas and Resource Book" (1995), and from an article in the Detroit News ("Our Lakes in Peril. Sources and Solutions" Aug 25, 1999).

This material has been compiled for educational use only, and may not be reproduced without permission.  One copy may be printed for personal use.  Please contact Randall Schaetzl ( for more information or permissions.