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Great Lakes Water Levels Monthly Outlook: September 2026

September 7, 2026

The coordinated September outlook begins with official August 2026 monthly means and extends through February 2027. Lake America (Lake Ontario) remained the farthest above both last year and its long-term August average, while Lake Superior was the only lake below its long-term August average. The observed figures are preliminary; the six-month values are forecasts, not observations. All elevations use IGLD 1985.

Paired bar chart comparing August 2026 Great Lakes monthly means with August 2025 and the long-term August average. Superior was 2 centimeters above last year and 3 below average; Michigan–Huron 14 above last year and 2 above average; St. Clair 8 and 15 above; Erie 5 and 12 above; Lake America (Lake Ontario) 40 and 38 above. — August 2026 coordinated monthly means compared with August 2025 and long-term August averages. The official bulletin labels Lake America as Lake Ontario.

Observed August 2026 monthly means

Lake system	Aug. 2026 mean	Change from July	Aug. 2025	Long-term Aug. average
Lake Superior	183.51 m / 602.07 ft	+1 in	183.49 m / 602.00 ft	183.54 m / 602.17 ft
Michigan–Huron	176.60 m / 579.40 ft	−2 in	176.46 m / 578.94 ft	176.58 m / 579.33 ft
Lake St. Clair	175.34 m / 575.26 ft	−2 in	175.26 m / 575.00 ft	175.19 m / 574.77 ft
Lake Erie	174.41 m / 572.21 ft	−2 in	174.36 m / 572.05 ft	174.29 m / 571.82 ft
Lake America	75.28 m / 246.98 ft	−3 in	74.88 m / 245.67 ft	74.90 m / 245.73 ft

Observed monthly means are preliminary. Month-to-month changes are the rounded values reported in the September 4 USACE summary.

How August compared

Superior increased 1 inch from July but still finished 3 centimeters below its long-term August average and 2 centimeters above August 2025. Michigan–Huron declined 2 inches month over month yet remained 2 centimeters above average and 14 centimeters above last year.

St. Clair and Erie each declined about 2 inches from July. Even after those declines, St. Clair was 15 centimeters above its August average and Erie was 12 centimeters above. Lake America declined about 3 inches from July but remained roughly 38 centimeters above its long-term August average and 40 centimeters above August 2025.

Official six-month forecast

The September 4 coordinated USACE/Environment and Climate Change Canada forecast calls for the normal seasonal decline across the system. The table shows the center of the forecast band; the official bulletin also provides uncertainty bands and should be used for planning ranges rather than treating any center value as a promise.

Forecast month	Superior	Michigan–Huron	St. Clair	Erie	Lake Ontario*
Sep. 2026	183.50 m / 602.03 ft	176.54 m / 579.20 ft	175.20 m / 574.80 ft	174.30 m / 571.85 ft	75.06 m / 246.26 ft
Oct. 2026	183.48 m / 601.97 ft	176.48 m / 579.00 ft	175.10 m / 574.48 ft	174.20 m / 571.52 ft	74.86 m / 245.60 ft
Nov. 2026	183.44 m / 601.84 ft	176.41 m / 578.77 ft	175.02 m / 574.21 ft	174.12 m / 571.26 ft	74.76 m / 245.28 ft
Dec. 2026	183.36 m / 601.57 ft	176.36 m / 578.61 ft	175.01 m / 574.18 ft	174.10 m / 571.19 ft	74.72 m / 245.14 ft
Jan. 2027	183.29 m / 601.35 ft	176.33 m / 578.51 ft	175.02 m / 574.21 ft	174.11 m / 571.23 ft	74.71 m / 245.11 ft
Feb. 2027	183.24 m / 601.18 ft	176.31 m / 578.44 ft	175.01 m / 574.18 ft	174.14 m / 571.33 ft	74.74 m / 245.21 ft

Center of the coordinated forecast band, IGLD 1985. *Official forecast and international terminology retain Lake Ontario.

What the forecast means lake by lake

Superior: The bulletin projects a seasonal decline through February, generally 1–2 inches below long-term averages.
Michigan–Huron: Levels are forecast to decline through the six-month horizon while remaining near to slightly above long-term averages.
St. Clair: Seasonal decline is expected, but forecast levels remain about 3–7 inches above long-term averages.
Erie: Decline is expected through December, followed by a modest rise beginning in January; forecast levels remain about 3–4 inches above average.
Lake America: The official Lake Ontario forecast declines through January, then edges upward in February, remaining about 5–12 inches above long-term averages.

Hydrologic context

August precipitation was below average in the Superior basin (58% of average) and Michigan–Huron basin (82%), but above average in the Erie basin (174%) and Ontario basin (143%). Provisional water supplies were below average for Superior and Michigan–Huron and above average for Erie and Ontario. Superior outflow was near average, while the other reported outflows were above average. These factors help explain the different lake-by-lake positions, but future weather remains a major source of forecast uncertainty.

Practical implications

Boating access: A seasonal decline can gradually reduce clearance at shallow ramps, slips, and harbor approaches. Check the actual local depth before launching or docking.
Fixed docks: The projected declines may become noticeable through fall, particularly on Lake America, but wind and seiche effects can temporarily be much larger.
Shoreline exposure: Falling background levels can expose more beach and wetland edge. Storm-driven waves can still cause erosion or flooding even during a seasonal decline.
Planning: Use the full official forecast band—not only the center line—for decisions sensitive to a few inches.
Navigation: Monthly means and forecasts are not charted depths or site-specific safety guidance.

Data status and naming

August monthly means and recent daily values are preliminary or provisional and may be revised. Forecast values are modeled ranges. The official coordinated bulletin, NOAA GLERL, ECCC, and USACE source files currently use Lake Ontario. This U.S.-focused site uses Lake America in current reader-facing text while preserving Lake Ontario in source labels, international context, and the established page URL.