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Where does Georgian Bay’s water come from and how does it fit with the rest of the Great Lakes?

All five Great Lakes (Lake Superior, Lake Michigan, Lake Huron, Lake Erie and Lake Ontario) are part of one large watershed and are closely connected with each other through various smaller lakes, rivers, and streams. Georgian Bay is located in the Northeastern portion of Lake Huron (Naadowewi-gichigami).

At the top of the watershed through about 200 rivers and the Long Lac and Ogoki diversions, water starts its journey in the Great Lakes by flowing into Lake Superior. Lake Superior water flows through the St. Marys River into Lake Huron. Connecting Lake Michigan and Lake Huron, the Straits of Mackinac maintain both lakes’ water levels in a state of near equilibrium. These two combined bodies of water are often referred to hydrologically as one lake - Lake Michigan-Huron. The Chicago Diversion diverts water away from Lake Michigan and the Great Lakes basin into the Upper Mississippi River basin. The St. Clair River drains from Lake Huron into Lake Erie, which then passes water into the Niagara River and over the 100 metre drop at Niagara Falls, flowing into Lake Ontario, and finally, into the St. Lawrence River. From the St. Lawrence River, water eventually empties out into the Atlantic Ocean.

Why do water levels change from year to year?

Historically, Lake Michigan–Huron water levels have fluctuated seasonally and vary annually over a 6.33-foot range. In recent years, however, seven-plus foot swings have been recorded, as record highs and lows in water levels have been driven by changes in climate resulting from global warming. From 1999 to January 2013, Georgian Bay experienced its longest stretch of low water levels. During this time, levels measured below the all-time historic low previously observed in 1964 and were 70 cm below the long-term seasonal average. In January 2013, the record low was set at 175.57 metres. This period was followed by the fastest ever recorded rise in water levels leading to a year of all-time highs in 2020, in which Lake Huron exceeded its record high monthly levels for eight months in a row from January to August. The previous record high was observed in 1986 at 177.50 metres.


In general, water levels are impacted by a variety of factors. GBF has identified several water level drivers, which include precipitation, evaporation, climate change, groundwater, connecting channels, diversions, control structures, and isostatic adjustment. Some, like precipitation and evaporation, have a significant impact on water conditions, while others like groundwater comparatively exert less of an effect. Click here to see how the factors impact water levels.


Climate change is especially significant in understanding recent extreme water level fluctuations. As our planet warms due to anthropogenic activity causing the greenhouse gas effect, increased energy in the atmosphere causes evaporation and precipitation to become more intense and less predictable, leading to higher highs and lower lows in water levels. Stronger and reoccurring storm surges are also expected to temporarily increase Georgian Bay’s water levels, particularly on the side wind is blowing towards.


The evaporative process is also beginning earlier due to warmer winters, which also result in warmer waters. Lake Superior, for instance, lost an extra 10 inches in 2011/2012 due to an early start evaporative season! 

Is there any way to predict the trends of water levels?

Although water levels fluctuate daily and sometimes even hourly, seasonally we have a reasonable expectation that water levels will start low in the spring and peak in the summer typically rising on average a foot or more.


Moreover, computational modelling systems can, with a degree of certainty, forecast waters levels. While these models can’t predict an exact water level on a specific future date, they can forecast a range for water levels within a certain confidence interval. For instance, models can say that typical water levels should range between one metre above or below an average level ninety-five percent of the time, which is known scientifically as the 95th-percent confidence interval.


It is important to keep in mind, however, that complex relationships between water level drivers and unpredictability make it hard for forecasters to predict water levels accurately beyond six months. Few modellers have produced long-term climate models that look forward 30, 50 and 70 years into the future because of these uncertainties, and the reliability of these studies remains to be seen. Past trends, moreover, no longer inform projections about future levels. However, as the only tools we have available, these models are increasingly being refined to smaller local scales and continuously assessed for their ability to predict conditions. As a result of extensive work in this area, researchers at Environment and Climate Change Canada believe that there are indications that future extreme highs and lows will frequently exceed past extreme levels.

How do fluctuations in water levels help maintain healthy wetlands and biodiversity?

Our native plants and animals have evolved and adapted to historic conditions in the upper Great Lakes. Seasonal variations in water supplies are generally predictable, allowing local plants to germinate in sun-warmed, wet soils and later grow as lake levels rise over the summer. Other plants grow in deeper water at the appropriate limits of sunlight penetration. On a gradually sloping, soft lakebed, these plants can naturally move towards or away from the shoreline to meet their ideal water level needs from year to year. The competitive success of such plants ensures that there is a variety of vegetation that can provide shelter, protection, and food for the large number of species that call Georgian Bay’s wetlands home. This biodiversity is important to the healthy functions of our coastal wetlands.


Let’s look at an example to better understand what happens to biodiversity and wetlands when water levels don't fluctuate. From 1998 to 2013, the Bay’s water levels sustained at record low conditions. Numerous coastal wetlands changed to meadows with fewer species, woody plants, and reduced ecological services. Some invasive species outcompeted native species moving into the exposed lakebed. As water returned to normal levels, recently sprouted shrubs and small trees started to die off providing structure and shelter and biodiverse wetlands remerged. GBF, partnered with NASA, and discovered that an overall 3% loss in Georgian Bay coastal wetlands was experienced during this 15-year period, but interestingly the northern portion of the Bay responded in a different way than the southern portion.

What control structures are in place or under consideration to manage GB water levels?

Currently, the only control structures impacting water levels in Georgian Bay are located on St. Mary’s River, which regulate inflows into Lake Michigan-Huron from Lake Superior. These structures are overseen by the International Lake Superior Board of Control, under the authority of the International Joint Commission (IJC). There are no control structures in place to regulate Lake Michigan-Huron outflows.


In 2016, GBF partnered with world-renowned AECOM Technical Services to investigate whether there are viable structural options to enhance climate resilience by controlling lake level conditions, particularly water leaving Lake Michigan-Huron through the St. Clair River or Lake Erie at the Niagara River. The study entailed the examination of over a dozen existing structural alternatives for water level control in use around the world, grouped into four main categories: Compensatory Structures, Power Generating Structures, Adaptive Management Structures and Other Structures.


The most important recommendation of AECOM’s team indicated that there is a need for governments to move forward with cost-effective ways of increasing climate resilience in the upper Great Lakes through the introduction of new water levels management tools.


AECOM’s evaluation of what these tools might look like culminated in the selection of three illustrative alternatives: Power generating structures, flexible control structures and re-naturalizing parts of the connecting channel between Lake Michigan-Huron and Lake St. Clair.


The three illustrative examples selected by the expert team as feasible elements of a potential mitigation response to climate change demonstrate that there are numerous positive impacts:


  • In-stream Turbines (Power generating structure): Could be installed on the riverbed of the Upper St. Clair River by the Blue Water Bridge, as well as upstream of the St. Marys River Compensation Works in Lake Superior. By reducing river flow when in operating mode, the turbines impact river hydrodynamics, increasing water levels upstream and decreasing levels downstream, as needs dictate and then when not needed can be feathered or possibly reversed to increase flows producing the opposite effect.

  • Inflatable Dams (Flexible control structure): Could be installed in the St. Clair River at Stag and/or Fawn Islands. When the inflated dams are operational, river flow is reduced with a resultant increase in upstream water levels. During higher than desired levels, the dams are deflated to allow for increased river flow.

  • Park Fill and Control Gates System (Re-naturalizing): Could be constructed at the mouth of St. Clair River. The proposed structure is composed of two new islands (involving stone revetment, sand fill, topsoil and landscaping) and two flood control gates that will be adjusted, as needed, to reduce river flow and increase upstream water levels. The gates can be opened to allow for increased river flow when water levels are higher than desired. The constructed islands would have positive environmental benefits (e.g., aquatic habitat, fish spawning reef).


Who controls the water levels in Georgian Bay?

There is no single organization that controls water levels in Georgian Bay, but there are a number of organizations that have an impact.


The Long Lac and Ogoki diversions, governed by the Ontario Power generation (OPG) in agreement with the Ontario Government and six First Nations bands, diverts most of the natural flow that used to go northwards into James Bay southward into Lake Superior. Originally designed to increase power production as part of the war effort, to this day, these two diversions are the only artificial diversions bringing almost twice the water into the Great Lakes than the Chicago Diversion flows out.


Control works on St. Mary’s River regulate inflows into Lake Michigan-Huron from Lake Superior, through three hydro dams, multiple locks, and the compensating works. The latter are overseen by the International Lake Superior Board of Control.


The Chicago Diversion, managed by the US Army Corps of Engineers (USACE), diverts water from the Lake Michigan watershed into the Upper Mississippi River.

What is the International Joint Commission and how do they impact water levels?

The International Joint Commission (IJC) was created by Canada and the United States in 1909 to settle disputes and manage and protect lake and river systems along the entirety of the common countries’ borders. The IJC’s two main responsibilities include approving projects that affect water levels and flows across the boundary and investigating transboundary issues to offer appropriate recommendations.


The IJC’s mission statement reads:


The International Joint Commission prevents and resolves disputes between the United States of America and Canada under the 1909 Boundary Waters Treaty and pursues the common good of both countries as an independent and objective advisor to the two governments.


In particular, the IJC rules upon applications for approval of projects affecting boundary or transboundary waters and may regulate the operation of these projects; it assists the two countries in the protection of the transboundary environment, including the implementation of the Great Lakes Water Quality Agreement and the improvement of transboundary air quality; and it alerts the governments to emerging issues along the boundary that may give rise to bilateral disputes.


Primarily, the IJC impacts Georgian Bay’s water levels through the regulation of the St. Marys River control structures according to Plan 2012. Plan 2012 is the current regulation strategy for Lake Superior. It provides a set of rules used to determine the amount of water to release or retain from the lake relative to what would have been the natural or “pre-project” flows, via the control structures located on the St. Marys River.


Plan 2012 adjusts water levels based on differences from seasonal targets, and considers pre-project flows – the natural flows prior to the construction of canals and other constructions before 1887. Control-structure operations at St. Marys must keep in mind different considerations and stakeholder needs in determining which gates to open and by how much, while respecting physical and operational limits. This process is called the Balancing Principle.

What is GBF’s water levels advocacy strategy?

Georgian Bay Forever strongly believes in the collaborative benefits of partnering on scientific research, restoration projects, and communication, and we work closely with other organizations to advocate for ecological and economic resiliency in the face of expected and increasing variability in water levels.


That’s why we believe it is important to support ongoing research and science to help understand these impacts and work towards mitigation solutions that help the ecosystem and economy. But that only treats the symptoms. Our work is also focused on educating the public with a balanced view of the available science on the larger issues, such as climate change and its impact on the Bay.


In October 2020, Georgian Bay Forever (GBF) and the Georgian Bay Association (GBA) held the 2020 Water Levels Symposium featuring scientific and policy experts. The purpose was to get to an expert consensus on what is driving extreme water levels and its volatility, and identify some gaps that need to be filled to help mitigate those extremes.


GBF and GBA held an additional water level symposium in 2021 that focused on impacts of extreme high/low water levels, and adaptation strategies for resilience. Given that the existing tools for mitigation were never designed with climate change in mind, there is no way that they can manage extreme water level fluctuations. Even the development of Plan 2012 gave rise to one dissenting opinion from the US Section Chair of the IJC who expressed the opinion that climate change impacts were not sufficiently weighted. Therefore, it is important to consider how else to adapt to these potential impacts, particularly in the context of the predicted effects that climate change will have on future water levels.


GBF and GBA also have made a number of joint deputations to municipalities on Georgian Bay to ensure that residents, businesses, ports, marinas and municipalities have the best information available. In light of emerging new water level models, we are encouraging municipal governments to consider raising the high-water mark accordingly when planning infrastructure, docks, coastal roads, boat launches and setbacks.


GBF is also actively advocating for the release a technical report by the Meteorological Service of Canada, a branch of Environment and Climate Change Canada (Seglenieks and Temgoua, 2021) and the highlights report with data visualizations by the Ontario Climate Consortium (OCC, 2021). These reports examine the likelihood that extreme high-water levels could be as much 3 feet higher than the last extreme high by the year 2100, gradually increasing over the next 80 years.


GBF is also advocating for the revival of the International Joint Commission (IJC) 2013 recommendation to put in place a Great Lakes Water Levels Advisory Board. A key and important role for a Great Lakes Advisory Board would be to integrate and fortify gaps in data through monitoring, measuring and modelling water levels in the Great Lakes to better inform government and citizens of changing conditions due to climate change.


GBF’s further current advocacy efforts focus on starting an official conversation and international discussion about these new expected realities and whether adaptations or additional new control structures at the mouth of the St. Clair and/or Niagara Rivers could aid in providing systemic resilience; continuing research for an improvement in the tools available to better mitigate extreme water conditions, including additional measures; examining the roll that the Great Lakes-St. Lawrence River Adaptive Management (GLAM) Committee could play in improving coordination between all control structures; and encouraging further investment in increasing data collection points and the application of available technology to improve the quality and quantity of data input feeding into the emerging new modelling.

Can you help me understand all the terms that are used to explain water levels?

Here is a list of commonly used terms:


Bathymetry: The measurement of water depth in oceans, seas, or lakes.


Climate: The prevailing weather trends in an area over a long period of time (typically 30 to 40 years).


Climate resilience: The capacity of a system to adapt to a range of climate-induced stressors to maintain and sustain ecological function and economic value over the long-term. Resilience is a trait representing the capacity of a system to cope with a hazardous event, trend, or disturbance, responding or reorganizing in ways that maintain essential functions, identity, and structure, while maintaining the capacity for adaptation, learning, and transformation (IPCC, 2014).


Ecological services: The benefits people obtain from healthy ecosystems.


Evaporation: Occurs when liquid, like water, is turned into vapour.


Greenhouse gas effect: Rising green-house gases like carbon dioxide, nitrous oxide, methane, and chlorofluorocarbons trap heat in the atmosphere, warming the planet.


Net Basin Supply (NBS): The sum of all inflowing and outflowing water to a system, such as the Great Lakes. Overlake precipitation and runoff are inflows, evaporation an outflow, and diversion and flows between lakes are both inflows and outflows. This equation can be represented visually:


  • Runoff (deposit) + Overlake precipitation (deposit) – Overlake evaporation (withdrawal) +/- Flow between lakes can be deposit or withdrawal +/- diversions between lakes can be deposit or withdrawal


NBS represents the total contribution of water to each lake, excluding inflows from upstream lakes, outflows to downstream lakes, and diversions into or out of the lakes, as shown in the graphic above. In other words, NBS represents the net influence of precipitation over the lake, runoff from a lake’s watershed into the lake, and evaporation from the lake’s surface. (Source USACE)


Overlake Precipitation: Any liquid or frozen water that forms in the atmosphere and falls directly on the lake’s surface. It comes in the forms of rain, snow, sleet, and hail.


Plan 2012: The current regulation strategy for control structures located on St. Marys River, which regulate Lake Superior’s outflows into Lake Michigan-Huron. Plan 2012 adjusts water levels based on the differences from seasonal targets, as well as considers flows prior the construction of canals and other constructions before 1897.


Precipitation: Any liquid or frozen water that forms in the atmosphere and falls to Earth’s surface. It comes in the forms of rain, snow, sleet, and hail.


Resilience: The ability to withstand or recover quickly from difficult conditions


Watershed: Land area which drains water into a specific waterbody or common outlet, like a river, lake, or bay. Watershed is sometimes used interchangeably with drainage basin.


Weather: The mix of events which happen each day in our atmosphere; what we see when we look outside.

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