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

Wet conditions prevent typical October water level declines on Lakes Erie and Ontario

During October, overall the Great Lakes basin experienced only slightly above average water supply conditions. However, both the Lake Erie and Lake Ontario basins received much more precipitation than average.

The average level of Lake Superior in October was 3 cm below average and 27 cm below last year’s level. The October water level of Lake Michigan-Huron was 42 cm above average and 37 cm lower than last year. Lake Erie’s water level was 5 cm lower than the same time last year, but still 58 cm above average, making it the fourth highest October level on record. Lake Erie also experienced its second highest beginning of November level on record and second largest October water level rise. The average October water level for Lake Ontario was 16 cm above the long-term October average and 8 cm higher than last year. Lake Ontario experienced its third largest October water level rise during the period of record.

At this time of year, all the lakes are typically continuing their seasonal decline, however, due to wet conditions, both Lake Erie and Lake Ontario saw rises in October when they would normally decline. 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.

October monthly levels

Lake Superior’s monthly mean level was 183.49 m (IGLD85^{Footnote 1} ), 3 cm below average and 27 cm lower than this time last year.

Lake Michigan-Huron’s monthly mean level in October was 176.88 m (IGLD85). This was 42 cm above its October monthly mean water level and 37 cm lower than last year.

Lake Erie had an average monthly water level of 174.67 m (IGLD85), 58 cm above average and 5 cm below last year’s level. This is Lake Erie’s fourth highest October water level on record.

Lake Ontario’s October monthly mean level was 74.78 m (IGLD85), 16 cm above average and 8 cm higher than the level from a year ago.

Lake level changes

Lake Superior declined by 5 cm in October, close to twice its typical October decline of 3 cm.

Lake Michigan-Huron declined by 4 cm, close to half its average decline of 7 cm.

Lake Erie rose by 8 cm, at a time when it typically declines by 9 cm. This is the second largest water level rise on record for the month.

Lake Ontario’s level increased by 8 cm in October, at a time when the lake typically declines by 11 cm. This is the third largest October rise during the period of record (1918-2020).

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

Beginning-of-November lake levels

Lake Superior’s beginning-of-November level was 6 cm below average, which is 29 cm lower than last year.

Lake Michigan–Huron’s level was 42 cm above average at the beginning of November and 38 cm lower than this time last year.

Lake Erie was 67 cm above average at the beginning of November and 4 cm higher than last year at this time. This is the second highest beginning of November level on record.

Lake Ontario’s level at the start of November was 27 cm above average and 20 cm higher than this time last year. 

At the beginning of November, all of the Great Lakes were at least 24 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).

Water levels forecast

At this time of year, all the lakes are typically continuing their seasonal decline. 

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 above average.

The level of Lake Michigan-Huron is expected to decline throughout the fall under all water supply conditions, but it is expected to remain well above 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 fall and winter 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.

Fall and winter storms

The fall and winter can bring higher waves and storm surges on the Great Lakes. Winds blowing across long open water sections, or fetch, can cause large waves and push water levels up on the downwind side of the lakes.

The largest waves occur on Lake Superior, where wave heights may approach 9 m. The largest storm surge occurs on Lake Erie, with the largest being about 2.5 m. Although waves and storm surges are usually well below these maximums, they can create rapid changes in water levels that should be considered when undertaking activities on the shores of the Great Lakes.

In the coming months, the above-average levels of lakes Erie, Michigan–Huron and Ontario could increase the potential for erosion of some shorelines, especially steep shoreline bluffs made up of silts, sands, gravels and cobbles that are exposed to waves. Although erosion around the Great Lakes can cause significant changes to the shoreline that can impact property and activities around the lakes, it is also a naturally occurring process that helps support shoreline dynamics such as beach building and the natural ecosystem of the Great Lakes.

Keep in mind that conditions can change quickly along the shores of the lakes and this can lead to dangerous conditions, especially if you are not prepared.  So be sure to check the local forecasts and always keep a safe distance from the shoreline edge.

^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