Water levels forecast

The water levels forecast for Lake Superior, Huron, St. Clair, Erie and Ontario, and Montréal Harbour. Monthly mean water levels are reflective of International Great Lake Datum (1985), which refers to metres above chart datum. Data also references exceedance probability.

On this page

• About monthly mean lake levels
• Lake Superior
• Lake Huron
• Lake St. Clair
• Lake Erie
• Lake Ontario
• Montréal Harbour

About monthly mean lake levels

The forecast of monthly mean lake levels for the next 6 months are grouped as:

• high level, where there's a 5% probability of exceeding this level
• most probable level, where there's a 50% probability of exceeding this level
• low level, where's there's a 95% probability of exceeding this level

Canada and U.S. flag water levels are collected by the:

• Canadian Hydrographic Service for the Canadian gauges
• National Ocean Service and National Oceanic Atmospheric Administration for the American gauges

The probable range of future levels for 6-month forecasts are prepared under the auspices of the International Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data by:

• Environment Canada
• the U.S. Army Corps of Engineers, Detroit District
• Great Lakes-St. Lawrence Regulation Office in Cornwall

Lake Superior

Chart datum 183.20m International Great Lake Datum (1985).

Lake Huron

Chart datum 176.00m International Great Lake Datum (1985).

Lake St. Clair

Chart datum 174.40m International Great Lake Datum (1985).

Lake Erie

Chart datum 173.50m International Great Lake Datum (1985).

Lake Ontario

Chart datum 74.20m International Great Lake Datum (1985).

Montreal Harbour

Chart datum 5.55m International Great Lake Datum (1985).