Monthly Water Level Bulletin
A newsletter, LEVELnews published by Environment Canada is included with the bulletin.
A network of gauging stations on both sides of the border on each lake is used to determine the average water level for the month. The following stations are used:
Lake Superior at: Thunder Bay, Michipicoten, Duluth, Marquette and Point Iroquois
Lakes Michigan/Huron at: Thessalon, Tobermory, Milwaukee, Ludington, Mackinaw City and Harbor Beach
Lake St. Clair at: Belle River and St. Clair Shores
Lake Erie at: Port Stanley, Port Colborne, Toledo and Cleveland
Lake Ontario at: Port Weller, Toronto, Cobourg, Kingston, Rochester and Oswego
Additional Sources of Information:
- The Great Lakes St. Lawrence River System
- Natural Factors Affecting Lake Levels
- Fluctuations in Lake Levels - types
- Circulation in the Great Lakes
- Datums - explanation of datums used for water levels and navigational charts
- US Army Corps of Engineers – Detroit District
Great Lakes and Montreal Harbour
Monthly Bulletin prepared by the Canadian Hydrographic Service Fisheries and Oceans Canada
Water Level Advisory
Water levels for Lake Superior, Lake Michigan-Huron, Lake St. Clair, Lake Erie, Lake Ontario and Montréal Harbour are above their all-time average for this time of year and are above the level of Chart Datum.
Mariners should exercise extreme caution throughout the entire system, especially during periods of strong winds when water levels can rise or fall significantly in a short period of time.
|April 2021||Lake Superior||Lake Huron||Lake St. Clair||Lake Erie||Lake Ontario||Montréal|
|Mean for Month (preliminary data)||183.48||176.95||175.54||174.63||74.62||6.54|
|Mean for month last year||183.62||177.30||175.91||175.05||75.32||8.04|
|Mean for month, last 10 years||183.31||176.48||175.29||174.48||74.99||7.37|
|Statistics for period of record||1918-2020||1918-2020||1918-2020||1918-2020||1918-2020||1967-2020|
|Maximum monthly mean / year||183.68
|Mean for month, All Time||183.27||176.40||175.06||174.24||74.89||7.45|
|Minimum monthly mean / year||182.72
|Probable mean for next month||183.56||176.98||175.56||174.66||74.72||6.33|
To convert from metres to feet, divide by 0.3048
The monthly mean levels for the previous year and current year shown on the graphs are the average of water levels recorded at a network of gauging stations on each lake. Historical data from these networks are used to determine the all-time average and the historical extreme monthly levels.
Water levels for the Canadian stations in the networks are collected by the Canadian Hydrographic Service. Six month forecasts of the probable range of future levels are prepared under the auspices of the International Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data by Environment Canada and the Detroit District, Corps of Engineers.
This bulletin is prepared each month as a public service and is available on the World Wide Web at:
Additional information on water levels in the Great Lakes System may be obtained by telephoning the Canadian Hydrographic Service at (877) CHS-LINK (877-247-5465), by fax at (905) 336-8916, or by email at CATCWL@dfo-mpo.gc.ca
- Date Modified: