LEVELnews: Great Lakes and St. Lawrence River water levels, December 2021

Dry conditions result in significant water level declines on Lake Superior, Lake Michigan-Huron, and Lake Erie

During November, overall the Great Lakes basin experienced below average water supply conditions resulting in significant declines of lake levels on some lakes. Of note, the Lake Erie basin received close to half its typical November precipitation and the outflow from Lake Superior was its lowest since May 2013.

The average level of Lake Superior in November was 10 cm below average and 33 cm below last year’s level. The November water level of Lake Michigan-Huron was 37 cm above average and 43 cm lower than last year. The dry month resulted in a decline in Lake Erie water levels with the monthly average for Lake Erie 2 cm lower than this time last year but still 61 cm above average, this is the fifth highest November level on record and it was also the lake’s sixth highest beginning of December water level. The average November water level for Lake Ontario was 32 cm above the long-term November average and 26 cm higher than last year. Lakes Superior, Michigan-Huron, and Erie experienced their third, second, and sixth largest November water level declines during the period of record, respectively.

Relative to their beginning-of-December levels and with average water supplies for this time of year, some of the lakes are expected to continue their seasonal decline while others may hold steady or begin their seasonal rise in the coming months. The water levels of Lake Superior are expected to remain below average under typical water supply conditions. Wetter than average conditions could result in Lake Superior levels increasing above average and drier than typical conditions may result in levels moving further below average. The water levels of Lakes Michigan-Huron and Erie are expected to remain above average under any water supply scenario. Lake Ontario levels are above average and are expected to remain so under average conditions. In the event of wetter or drier than average conditions, Lake Ontario has the potential to rise well above average by mid-winter, whereas drier than average conditions could result in lower than average levels.

With water levels remaining above average on some lakes and the possibility of large storms and winds during the fall and winter months, low-lying areas are at risk for accelerated coastline erosion and flooding. For current information and forecasts, please refer to the sources listed below.

November monthly levels

Lake Superior’s monthly mean level was 183.38 m (IGLD85^{Footnote 1} ), 10 cm below long-term average (1918-2020) and 33 cm lower than this time last year.

Lake Michigan-Huron’s monthly mean level in November was 176.77 m (IGLD85). This was 37 cm above its November monthly mean water level and 43 cm lower than last year.

Lake Erie had an average monthly water level of 174.63 m (IGLD85), 61 cm above average and 2 cm below last year’s level. This is Lake Erie’s fifth highest November water level on record.

Lake Ontario’s November monthly mean level was 74.86 m (IGLD85), 32 cm above average and 26 cm higher than the level from a year ago.

Great Lakes Water Level Information: November 2021 Monthly Mean Level

Lake	Compared to Monthly Average (1918–2020)	Compared to November 2020
Superior	10 cm below	33 cm below
Michigan–Huron	37 cm above	43 cm below
St. Clair	55 cm above	17 cm below
Erie	61 cm above	2 cm below
Ontario	32 cm above	26 cm above

Lake level changes

Lake Superior declined by 12 cm in November, more than twice its typical November decline of 5 cm. This is the third largest November water level decline in the period of record (1918-2020), which is mostly a result of record low water supplies coming into the lake.

Lake Michigan-Huron declined by 13 cm, also more than double its average decline of 5 cm. This is the second largest water level decline on record for the month.

Lake Erie declined by 14 cm, more than triple its average decline of 4 cm. This is the sixth largest water level decline on record for the month.

Lake Ontario’s level increased by 2 cm in November, at a time when the lake typically declines by 3 cm.  This is partly due to near record high inflows coming from Lake Erie.

(Note that lake level changes are based on the levels at the beginning of the month and not the monthly average levels.)

Beginning-of-December lake levels

Lake Superior’s beginning-of-December level was 13 cm below average, which is 38 cm lower than last year.

Lake Michigan–Huron’s level was 34 cm above average at the beginning of December and 45 cm lower than this time last year.

Lake Erie was 57 cm above average at the beginning of December and 7 cm lower than last year at this time. This is the sixth highest beginning of December level on record.

Lake Ontario’s level at the start of December was 32 cm above average and 26 cm higher than this time last year. 

At the beginning of December, all of the Great Lakes were at least 12 cm above their chart datum level. Chart datum is a reference elevation for each lake that provides more information on the depth of water for safe boat navigation on the lakes. For more information, please visit Low Water Datum – Great Lakes Coordinating Committee (greatlakescc.org).

Great Lakes Water Level Information: Beginning-of-December 2021

Lake	Compared to Beginning-of-Month Average (1918–2020)	Compared to December 2020
Superior	13 cm below	38 cm below
Michigan–Huron	34 cm above	45 cm below
St. Clair	53 cm above	26 cm below
Erie	57 cm above	7 cm below
Ontario	32 cm above	26 cm above

Water levels forecast

Relative to their beginning-of-December levels and with average water supplies for this time of year, some of the lakes are expected to continue their seasonal decline while others may hold steady or begin their seasonal rise in the coming months.

Lake Superior is currently below its average level and is expected to remain so under average conditions. Drier than average conditions could result in lake levels dropping further below average in the coming months, while wetter than average conditions may result in lake levels moving just above average.

The level of Lake Michigan-Huron is currently well above average and expected to remain so under average and wetter than average water supply conditions. In the event of drier than average conditions, lake levels could approach average.

Lake Erie levels are currently well above average and are expected to remain high under average and wetter than average water supply conditions. In the event of dry conditions, lake levels could approach average in the next six months.

Lake Ontario levels are above average and are expected to remain so under typical water supply conditions. Drier than average conditions could result in Lake Ontario levels falling below average, while wetter than average conditions may result in lake levels rising well above average throughout the winter and spring months.

For more information on the probable range of water levels, consult this page. 

For a graphical representation of recent and forecasted water levels on the Great Lakes, refer to the Canadian Hydrographic Service’s Monthly Water Levels Bulletin.

Great Lakes system profile    

The figure below shows the cross-section of the Great Lakes from Lake Superior to the Atlantic Ocean. Note that the vertical scale is exaggerated making the lakes appear deeper relative to their size.

As indicated in the figure, water originating in Lake Superior discharges through the St. Marys River to Lake Michigan-Huron. Water flows out of Lake Michigan-Huron through the St. Clair River to Lake St. Clair then downstream into the Detroit River and Lake Erie. Water leaving Lake Erie travels through the Niagara River and over Niagara Falls and into Lake Ontario. Lakes Superior, Michigan-Huron, and Erie are referred to as the upper Great Lakes due to the difference in lake surface elevations when compared to Lake Ontario. Water travels out of Lake Ontario and makes its way down the St. Lawrence River and discharges to the Gulf of St. Lawrence, then finally to the Atlantic Ocean.

Only two locations within the basin have structures that have a major impact on how much water flows from one body of water to the next, which include:

1. Several structures at the outlet of Lake Superior, including the Soo Locks, three hydropower facilities (one in Canada and two in the United States), and the “Compensating Works” at the head of the St. Marys Rapids. The International Lake Superior Board of Control is responsible for managing the outflow of Lake Superior and allocating flow to these various structures on the St. Marys River.
2. There are a second set of structures on the St. Lawrence River, which influence the flow of water from Lake Ontario. The primary structure is the Moses-Saunders Power Dam, which is jointly owned by Canada and the United States and spans Cornwall, Ontario and Massena, New York. The Long Sault Dam spillway is a secondary structure that is used primarily when the Moses-Saunders Dam is undergoing maintenance activities, but is not used for hydroelectric generation. There are also several Seaway locks. The International Lake Ontario – St. Lawrence River Board is responsible for managing the outflow of Lake Ontario and oversees the operation of these structures on the St. Lawrence River. The Beauharnois Hydroelectric Generating Station is located downstream of the Moses-Saunders Dam and is operated by Hydro-Quebec.

There are also some structures which can effect the amount of flow locally, but have no effect on the total overall amount of outflow.  These include the Iroquois Dam located upstream of the Moses-Saunders Dam on the St. Lawrence River and the International Niagara Control Dam (INCD) upstream of Niagara Falls on the Niagara River.  For example the INCD can divert some of the water around Niagara Falls and into reservoirs so that it can be used later to generate power. However, there is no control on the total amount of water that flows out of Lake Erie and into Lake Ontario as the partial structure only affects the amount of water flowing over the falls or to the reservoirs at different times of the day.

Look out for part two of this article in a future edition of LEVELNews when we will highlight some more interesting facts about the movement of water through the Great Lakes system.

November Precipitation over the Great Lakes ^a,b

Lake	%
Great Lakes Basin	70%
Superior	87%
Michigan-Huron	67%
Erie (including Lake St. Clair)	54%
Ontario	72%

November Outflows from the Great Lakes ^a

Lake	%
Superior	85%
Michigan-Huron	113%
Erie	126%
Ontario	123%

^a As a percentage of long-term average.
^b United States Army Corps of Engineers (GLP-LastMonth.pdf (army.mil))

Note: The figures contained in this report are provisional and are subject to change. Data are calculated from the best available observations at the time of posting.

Information on flooding

With water levels remaining high on some of the lakes, the risk of flooding is also high. Great Lakes water levels are difficult to predict weeks in advance due to natural variations in weather. To stay informed about Great Lakes water levels and flooding, visit the Ontario flood forecasting and warning program website at https://www.ontario.ca/flooding.

Additional information can also be found on the International Lake Superior Board of Control website, and the International Lake Ontario–St. Lawrence River Board website.

Information on current water levels and marine forecasts

Daily levels: Current daily lake-wide average levels of all the Great Lakes are available on the Great Lakes water levels and related data webpage by clicking on “Daily water levels for the current month”. The daily average water level is an average taken from a number of gauges across each lake and is a good indicator of the overall lake level when it is changing relatively rapidly due to recent high precipitation.

Hourly levels: Hourly lake levels from individual gauge sites can be found at the Government of Canada Great Lakes Water Level Gauging Stations website at Region - Tides, Currents, and Water Levels. These levels are useful for determining real-time water levels at a given site, however, it should be noted that they are subject to local, temporary effects on water levels such as wind and waves.

Marine forecasts: A link to current Government of Canada marine forecasts for wave heights for each of the Great Lakes can be found on the Great Lakes water levels and related data webpage under the “Wave and wind data heading”. Current marine forecasts for Lakes Superior, Huron, Erie and Ontario are available by clicking on the link of the lake in which you are interested. To view a text bulletin of recent wave height forecasts for all of the Great Lakes, click on the “Text bulletin wave height forecasts for the Great Lakes and St. Lawrence River” link. 

For more information:

Frank Seglenieks (Editor) and Nicole O’Brien
Boundary Water Issues
Meteorological Service Canada
Environment and Climate Change Canada
Burlington, ON L7S 1A1

Email: ec.LEVELnews-infoNIVEAU.ec@ec.gc.ca