LEVELnews: Great Lakes and St. Lawrence River water levels, March 2025

All the lakes start March below average for the first time in over a decade

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.

Historically, only Lake Superior would be declining at this time of year, and all other lakes would be nearing or beginning a rise in water levels.

Low-lying areas are at risk for accelerated coastline erosion and flooding due to an increased possibility of large storms and stronger winds in the winter months. For current information and forecasts, please refer to the sources listed at the end of this newsletter.

With greater ice coverage on the Great Lakes this year than in the past, there is growing interest in ice conditions. Find out where to get information on ice conditions below.

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 March, all the Great Lakes except Lake Superior, were at least 10 cm above their chart datum level. Lake Superior started March 12 cm below chart datum.  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 water level and is expected to remain so under most water supply conditions. Lake Superior could approach average water levels if it receives very wet water supply conditions over the next 6 months.

Lake Michigan-Huron ended the month below its average water level and is expected to remain so under most water supply conditions.

Lake Erie is expected to remain close to average if the lake receives average water supplies over the next 6 months.

Like Lakes Superior and Michigan-Huron, Lake Ontario also ended the month below its average water level. Water levels are expected to remain below average under dry or average water supply conditions. However, wetter than average water supply conditions may result in above average lake levels in the next few months.

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 the 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.

Where to get Great Lakes ice information?

Environment and Climate Change Canada monitors ice conditions in five regional areas, including the Great Lakes. If you would like to track ice conditions throughout the winter, please visit the Canadian Ice Service website.

If you click on the Great Lakes map on the regional area map provided, you will find several ice information products for the Lakes. This includes Ice Charts (showing ice concentrations and stages of development), Ice Hazard Bulletins, Ice Forecasts, and Ice Cover Graphs. You can also view high resolution maps showing the latest ice cover in Canadian waters nation-wide and animation of the changes in ice cover over the past 10 days. Be sure to look at the Ice Products Guide provided on the Canadian Ice Services website to learn more about the ice products and how to interpret them. The links to the product guide and the high-resolution maps can be found below the regional area map.

Flood information

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.

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: A monthly water level bulletin, produced by Fisheries and Oceans Canada, is available at: 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 is intended to complement the information provided by LEVELnews on a monthly basis.

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. 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 on the Government of Canada Great Lakes Water Level Gauging Stations website. 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 website 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.