LEVELnews: Great Lakes and St. Lawrence River water levels, April 2023

Moving into the spring, all the Great Lakes water levels remain above average

During March, the Great Lakes Basin experienced the following:

• The mean monthly water levels of all the Great Lakes were above average.
• Lake Superior experienced drier than average water supply conditions (a combination of the precipitation, evaporation, and runoff), unlike Lake Michigan-Huron, which experienced wetter than average water supply conditions. Water supply conditions for Lakes Erie and Ontario in March were near average.
• Lake Superior experienced a greater than average March decline, while Lake Michigan-Huron experienced an average rise. Lake Erie’s level rose slightly less than average and Lake Ontario experienced a somewhat above average rise.

This is the time of year when all lakes typically would be beginning their seasonal rise under average water supplies.

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

Unseasonably warm temperatures resulted in below average ice formation on the Great Lakes throughout the 2022-2023 ice season. A review of the ice conditions throughout this past winter is provided below.

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Great Lakes water level information:
March 2023 monthly mean levels

Lake	Levela	Compared to March monthly average   (1918–2021)	Compared to March 2022	Compared to record high (1918-2021)	Notes
Superior	183.43 m	19 cm above	27 cm above	18 cm below	-
Michigan–Huron	176.43 m	11 cm above	10 cm below	79 cm below	-
St. Clair	175.30 m	37 cm above	4 cm above	53 cm below	-
Erie	174.54 m	44 cm above	1 cm below	41 cm below	-
Ontario	74.88 m	19 cm above	11 cm below	49 cm below	-

^a Water levels are referenced to International Great Lakes (Vertical) Datum 1985 (IGLD85).  For more information, please visit International Great Lakes Datum Update – Great Lakes Coordinating Committee

Great Lakes water level information:
March lake level changes^a

Lake	March lake level change	March monthly average change (1918-2021)	Compared to average March change (1918-2021)	Notes
Superior	4 cm decline	1 cm decline	greater than average decline	-
Michigan–Huron	4 cm rise	4 cm rise	average rise	-
St. Clair	13 cm rise	17 cm rise	less than average rise	-
Erie	12 cm rise	13 cm rise	less than average rise	-
Ontario	15 cm rise	13 cm rise	greater than average rise	-

^a Lake level changes are based on the differences in levels at the beginning of the month and not the monthly average levels.

Great Lakes water level information:
Beginning-of-April level^a

Lake	Levela,b	Compared to April beginning-of-month average (1918–2021)	Compared to April 2021	Compared to record high (1918-2021)	Notes
Superior	183.42 m	18 cm above	24 cm above	20 cm below	-
Michigan–Huron	176.45 m	11 cm above	14 cm below	83 cm below	-
St. Clair	175.38 m	38 cm above	5 cm above	58 cm below	-
Erie	174.58 m	41 cm above	2 cm above	48 cm below	-
Ontario	74.98 m	21 cm above	10 cm below	51 cm below	-

^a At the beginning of April, all of the Great Lakes were at least 22 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.

^b Water levels are referenced to International Great Lakes (Vertical) Datum 1985 (IGLD85).  For more information, please visit International Great Lakes Datum Update – Great Lakes Coordinating Committee.

Water levels forecast

Lake Superior is currently above its average level and is expected to remain so under most water supply conditions.

Lake Michigan-Huron is expected to remain above average under most water supply conditions; very dry conditions would be required to bring the level below average at the end of the summer.

Lake Erie is expected to stay above average under all but extremely dry water supply scenarios.

Lake Ontario is above average and is expected to remain so under typical water supply conditions within the next few months. Water levels could move further above average if there are wetter than average water supply conditions.

Conversely, the levels could move below average if drier than average conditions prevail.

For more information on the probable range of water levels, consult the LEVELnews note on projections.

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.

March basin statistics

Lake	Precipitation (percentage of LTA)a,b	Net basin supply (probability of exceedance)c,d	Outflows (percentage of LTA)a
Superior	94%	69% (dry)	107%
Michigan-Huron	105%	42% (wet)	115%
Erie (including Lake St. Clair)	142%	52% (average)	118%
Ontario	135%	46% (average)	124%

^a As a percentage of long-term average (LTA).

^b Environment and Climate Change Canada – Canadian Precipitation Analysis System

^c <5% extremely wet; <25% very wet; <45% wet; 45-55% average; >55% dry; >75% very dry;    >95% extremely dry.

^d Please refer to the LEVELnews What is net basin supply for a description of net basin supply.

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.

The 2022-2023 lake ice season

With unseasonably warm temperatures for a majority of the winter season throughout the Great Lakes, it is not surprising that the ice content was well below average. Although a couple of cold air outbreaks in late December and early February over the lower lakes did temporarily cause a spike in ice coverage, these did not last very long. There were even a few days in mid-January when the overall ice coverage for all the Great Lakes was at it lowest level since records began in 1973.

Each of the Great Lakes is unique in its typical annual ice coverage. Lake Erie, typically has the highest ice coverage due to its shallow depth, and Lake Ontario generally has the lowest ice cover as it is very deep. Lake Ontario’s depth allows the lake to retain more heat and resist ice formation throughout the winter months. Lake Superior is the deepest of all the Great Lakes but has a much greater average ice cover due to colder average water temperatures from its northerly location.

The accompanying figures demonstrate Lake Erie and Lake Superior’s ice cover over the past three years.They show how much less ice there was in this past season with the exception of the cold air outbreaks on Lake Erie. This figure uses data from the Canadian Ice Service.

Around the Great Lakes, there were several environmental and economic effects of the low ice cover. With lower ice cover, recreational activities such as ice fishing and snowmobiling were impacted, as well as the businesses that rely on them.

Flood Information

With water levels remaining high on some lakes, there is a high risk of flooding. 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.

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 at Great Lakes - Daily Water Levels for This Month in Meters (army.mil). 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 Map. 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: Visit the Great Lakes water levels and related data webpage under the “Wave and wind data” heading for marine forecasts and wave heights. Current marine forecasts for Lakes Superior, Huron, Erie and Ontario are available as well as text bulletins of recent wave height forecasts.  

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: LEVELnews-infoNIVEAU@ec.gc.ca