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

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.

This is the time of year where all the lakes, except for Lake Superior, have typically peaked and have started their seasonal decline.

For updated current information and forecasts, please refer to the sources listed at the end of this newsletter.

This newsletter isn’t the only way to find about the Great Lakes, see below for other sources of Great Lakes information.

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 August, all the Great Lakes were at least 28 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

At the end of July, Lake Superior was below its average water level and is expected to remain so under most water supply conditions. Lake Superior could rise above average if it receives very wet water supply conditions over the next 6 months.

Lake Michigan-Huron was below its average water level at the end of July and is expected to remain there under most water supply conditions.

Lake Erie ended the month of July above average and is expected to remain so if the lake receives average or above average water supply conditions over the next 6 months. However, the level could also end up either above or below average, depending on future water supplies.

Lake Ontario ended the month of July close to average and is expected to remain close to or slightly above average under most water supply conditions.

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.

Other ways to keep up with what is happening in the Great Lakes

LEVELnews is just one way to keep up with what is happening in the Great Lakes. We have links to flooding, level, and forecast information below, but there are other ways to stay informed about the Great Lakes:

• Great Lakes Coordinating Committee website – Provides binationally coordinated data for water levels, flows, and net basin supply throughout the Great Lakes Basin
• Great Lakes Water Quality Agreement (GLWQA) information
• Quarterly Climate Impacts and Outlook – Archive of quarterly climate impacts and outlook documents that fulfill a commitment under the Climate Change Impacts (Annex 9) of the GLWQA
• Great Lakes Daily News – Keep up-to-date on Great Lakes news with articles curated by the Great Lakes Commission Staff
• Great Lakes Connection – A publication of the International Joint Commission focussing on the latest science, reader perspectives and opportunities to protect the health of the Great Lakes ecosystem
• International Lake Ontario–St. Lawrence River Board Weekly Summaries – Sign-up to receive the International Lake Ontario–St. Lawrence River Board's weekly summaries on Lake Ontario outflows

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 the Great Lakes, click on the “Text bulletin wave height forecasts for the Great Lakes and St. Lawrence River” link.