Update on Upcoming Outflows and Expected Conditions – July 2026
Date

The Board expects the total St. Marys River flow in July to be 2,310 m3/s (81,600 ft3/s) as prescribed by Regulation Plan 2012. This flow is near the long-term average for the month of July.

The gate setting of the Compensating Works at the head of the St. Marys Rapids will be adjusted to meet the Plan 2012-prescribed flow in July in consideration of capacity restrictions at the hydropower plants. On Thursday, July 2, Gates #9 through #12 will be raised slightly to a setting of 104 cm (41 in) open. Gate #1 will remain at its typical setting which supplies a flow of about 15 m3/s (500 ft3/s) to the channel north of the Fishery Remedial Dike and Gate #16 will remain partially open at a setting of 20 cm (7.9 inches) to facilitate sea lamprey trapping. The St. Marys Rapids flow will increase from approximately 488 m3/s (17,200 ft3/s) to approximately 507 m3/s (17,900 ft3/s) after gate adjustments. The setting is equivalent to approximately three gates fully open.

Water level changes over the month of June

  • The June 2026 water level rise of Lake Superior was 4 cm (1.6 in). The seasonal long-term average pattern is for Lake Superior to increase by 8 cm (3.1 in) in June.
  • From the beginning of June to the beginning of July, the level of Lake Michigan-Huron rose 5 cm (2.0 in) which matches its typical rise in June.

Water levels as of the end of June

As of the end of June, water levels for both lakes are within 3 cm (1.2 in) of their long-term averages.

  • The lake-wide average water level of Lake Superior is 3 cm (1.2 in.) below the seasonal long-term average (1918-2025) and 10 cm (3.9 in) above the level of a year ago. 
  • The lake-wide average water level of Lake Michigan-Huron is 3 cm (1.2 in) above the seasonal long-term average (1918-2025) and 15 cm (5.9 in) above the level of a year ago.

Forecast outlook in July

  • If weather and water supply conditions are near average, Lake Superior may rise by approximately 4 cm (1.6 in) and Lake Michigan-Huron may remain near its current level.
  • If conditions are much wetter than average, Lake Superior may increase by approximately 11 cm (4.3 in) and Lake Michigan-Huron may rise by approximately 6 cm (2.4 in).
  • If conditions are much drier than average, the water level of Lake Superior may decrease by 1 cm (0.4 in), and Lake Michigan-Huron may decrease by about 5 cm (2.0 in).

The International Lake Superior Board of Control is responsible for managing the control works on the St. Marys River and regulating the outflow from Lake Superior into Lake Michigan-Huron. Under any outflow regulation plan, the ability to regulate the flow through the St. Marys River does not mean that full control of the water levels of Lake Superior and Lake Michigan-Huron is possible. This is because the major factors affecting water supply to the Great Lakes (i.e. precipitation, evaporation, and runoff) cannot be controlled and are difficult to accurately predict. Outflow management cannot eliminate the risk of extreme water levels occurring during periods of severe weather and water supply conditions. Actual flows will vary hour-to-hour and day-to-day depending on hydrologic conditions and variations in flow at the hydropower facilities. Additional information can be found on the Board’s homepage: https://ijc.org/en/lsbc.