LEVELnews: Great Lakes and St. Lawrence River water levels, October 2024

Lakes Superior, Michigan-Huron, and Erie experience dry water supply conditions in September

In September, the Great Lakes Basin experienced the following:

• The mean monthly water level of Lake Superior was below average, while lakes Michigan-Huron, Erie, and Ontario were above average
• Lakes Superior, Michigan-Huron, and Erie experienced very dry to dry water supply conditions, while Lake Ontario experienced wet water supply conditions (a combination of the precipitation, evaporation, and runoff)
• The Lake Superior, Michigan-Huron, and Erie Basins received approximately half of the average September precipitation; the Lake Ontario Basin received precipitation amounts closer to average
• All the Great Lakes experienced an average or greater than average monthly decline

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

Low-lying areas are at risk for accelerated coastline erosion and flooding with water levels remaining above average on some lakes and with the increased possibility of large storms and stronger winds in the fall months. For current information and forecasts, please refer to the sources listed at the end of this newsletter.

Now that the Great Lakes have experienced their 2024 peak, we can look at how their seasonal rises compared to the average levels. Read more about it below.

Get notified when a new edition of LEVELnews is available!

Did you know that you can be notified whenever a new edition of LEVELnews is available? Visit the LEVELnews subscription page to sign up for email notifications. You can unsubscribe at any time.

¹ 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.

¹ Lake level changes are based on the differences in levels at the beginning of the month, not the monthly average levels.

¹ At the beginning of October, all the Great Lakes were at least 21 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.

² 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 ended the month below its average level and is expected to remain below average under most water supply conditions.

Lake Michigan-Huron is expected to remain close to average under typical water supply conditions, while drier than average conditions would result in lake levels falling below average. On the other hand, wetter than average conditions would lead to continued higher than average levels within the next few months.

Lake Erie’s level is expected to stay above average under most water supply scenarios. It would take very dry water supply conditions for lake levels to fall below average by the end of the year.

Lake Ontario water levels are expected to remain near average under typical water supply conditions. However, wetter than average water supply conditions may result in above average lake levels, whereas drier than average water supply conditions would result in the level moving below average.

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.

¹ As a percentage of long-term average (LTA).

² Environment and Climate Change Canada – Canadian Precipitation Analysis System. For more information, please visit: Technical documentation: Regional Deterministic Precipitation Analysis

³ <5% extremely wet; <25% very wet; <45% wet; 45-55% average; >55% dry; >75% very dry; >95% extremely dry.

⁴ Please refer to the LEVELnews – What is net basin supply for a description of net basin supply.

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

Summary of the 2024 seasonal rise

The timing of the seasonal rise varies from lake to lake. Lake Superior typically experiences its peak levels in late summer or early fall, whereas Lakes Michigan-Huron, Erie, and Ontario peak slightly earlier in mid-summer (June or July). Lake Superior has now likely seen its highest level of the season, while the other lakes are continuing their seasonal descent. So, with all the lakes past their peaks, we can now look at how the seasonal rise through the spring and summer in the lakes compared to their averages.

Lake Superior experienced a close to typical rise this year, but peaked in July, which is earlier than its typical peak in late summer or early fall. Lake levels have remained close to or less than average since the beginning of 2024.

Lake Michigan-Huron experienced close to its typical rise and peaked in July, which is its typical peak timing. The lake levels have remained above average throughout 2024.

Lake Erie experienced a bit less than its usual seasonal rise and peaked in July, which is typically when it peaks. Lake Erie levels started the year above average and have remained well above average throughout 2024.

Lake Ontario levels experienced less than its average seasonal rise and had a slightly delayed peak in August, which is later than its typical peak in July. Lake Ontario water levels have fluctuated slightly above and slightly below average throughout 2024.

Overall, all the lakes saw relatively typical seasonal rise patterns, except for Lake Superior, which peaked in July, and then experienced a rapid decrease in lake levels for the rest of the summer and early fall.

Flood information

With water levels remaining high on some lakes, there is a 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

Monthly levels: Fisheries and Oceans Canada produces the Monthly Water Level Bulletin for the Great Lakes and Montréal Harbour. On this page you will find a link to the full bulletin PDF. This publication complements the information provided by LEVELnews monthly.

Daily levels: Current daily average levels of all the Great Lakes are available at Great Lakes – Daily Water Levels for This Month in Meters. The daily average water level is taken from several gauges across each lake and is a good indicator of the overall lake level despite local rises or falls in water levels owing to factors like high precipitation, wind and waves.

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 “Wave and wind data” section of the Great Lakes water levels and related data webpage 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
National Hydrological Service
Meteorological Service of Canada
Environment and Climate Change Canada
Burlington, ON  L7S 1A1

Email: LEVELnews-infoNIVEAU@ec.gc.ca