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.

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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).

Month 5% Most probable 95%
March 2024 183.24 (0.04) 183.20 (0.00) 183.19 (-0.01)
April 2024 183.32 (0.12) 183.24 (0.04) 183.18 (-0.02)
May 2024 183.44 (0.24) 183.32 (0.12) 183.25 (0.05)
June 2024 183.56 (0.36) 183.40 (0.20) 183.31 (0.11)
July 2024 183.64 (0.44) 183.46 (0.26) 183.36 (0.16)
August 2024 183.68 (0.48) 183.50 (0.30) 183.38 (0.18)

Lake Huron

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

Month 5% Most probable 95%
March 2024 176.45 (0.45) 176.40 (0.40) 176.37 (0.37)
April 2024 176.58 (0.58) 176.46 (0.46) 176.38 (0.38)
May 2024 176.70 (0.70) 176.54 (0.54) 176.43 (0.43)
June 2024 176.80 (0.80) 176.60 (0.60) 176.46 (0.46)
July 2024 176.85 (0.85) 176.63 (0.63) 176.46 (0.46)
August 2024 176.84 (0.84) 176.61 (0.61) 176.42 (0.42)

Lake St. Clair

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

Month 5% Most probable 95%
March 2024 175.32 (0.92) 175.22 (0.82) 175.10 (0.70)
April 2024 175.44 (1.04) 175.26 (0.86) 175.07 (0.67)
May 2024 175.50 (1.10) 175.31 (0.91) 175.14 (0.74)
June 2024 175.54 (1.14) 175.34 (0.94) 175.15 (0.75)
July 2024 175.55 (1.15) 175.34 (0.94) 175.15 (0.75)
August 2024 175.52 (1.12) 175.30 (0.90) 175.08 (0.68)

Lake Erie

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

Month 5% Most probable 95%
March 2024 174.52 (1.02) 174.43 (0.93) 174.37 (0.87)
April 2024 174.70 (1.20) 174.51 (1.01) 174.39 (0.89)
May 2024 174.76 (1.26) 174.55 (1.05) 174.39 (0.89)
June 2024 174.76 (1.26) 174.54 (1.04) 174.36 (0.86)
July 2024 174.72 (1.22) 174.51 (1.01) 174.30 (0.80)
August 2024 174.65 (1.15) 174.44 (0.94) 174.22 (0.72)

Lake Ontario

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

Month 5% Most probable 95%
March 2024 74.90 (0.70) 74.76 (0.56) 74.68 (0.48)
April 2024 75.17 (0.97) 74.96 (0.76) 74.79 (0.59)
May 2024 75.41 (1.21) 75.07 (0.87) 74.82 (0.62)
June 2024 75.48 (1.28) 75.06 (0.86) 74.82 (0.62)
July 2024 75.35 (1.15) 74.97 (0.77) 74.73 (0.53)
August 2024 75.18 (0.98) 74.86 (0.66) 74.65 (0.45)

Montreal Harbour

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

Month 5% Most probable 95%
March 2024 7.32 (1.77) 6.70 (1.15) 6.27 (0.72)
April 2024 7.89 (2.34) 7.15 (1.60) 6.30 (0.75)
May 2024 7.95 (2.40) 7.00 (1.45) 6.19 (0.64)
June 2024 7.56 (2.01) 6.69 (1.14) 6.04 (0.49)
July 2024 7.10 (1.55) 6.50 (0.95) 5.84 (0.29)
August 2024 6.83 (1.28) 6.31 (0.76) 5.64 (0.09)