Update on Upcoming Outflows and Expected Conditions – June 2026
Date

The Board expects the total St. Marys River flow in June to be 2,270 m3/s (80,200 ft3/s) as prescribed by Regulation Plan 2012. This flow is near the long-term average for the month of June.

The gate setting of the Compensating Works at the head of the St. Marys Rapids will be decreased from the current setting equivalent to approximately four gates open to a setting equivalent to approximately three gates open, to meet the Plan 2012-prescribed flow in June in consideration of capacity restrictions at the hydropower plants. On Monday, June 8, Gates #9 through #12 will be lowered to a setting of 99 cm (39 in) open. Gate #16 will be raised to 20 cm (8 in) to allow sea lamprey trapping. 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. The St. Marys Rapids flow will decrease from approximately 539 m3/s (19,000 ft3/s) to approximately 488 m3/s (17,200 ft3/s) after gate adjustments.

Water level changes over the month of May

  • The May 2026 water level rise of Lake Superior was 8 cm (3.1 in). The seasonal long-term average pattern is for Lake Superior to increase by 10 cm (3.9 in) in May.
  • From the beginning of May to the beginning of June, the level of Lake Michigan-Huron rose 7 cm (2.8 in). The seasonal long-term average pattern is for Lake Michigan-Huron to increase by 8 cm (3.1 in) in May.

Water levels as of the beginning of June

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

  • At the beginning of June, the lake-wide average water level of Lake Superior is at the seasonal long-term average (1918-2025) and 12 cm (4.7 in) above the level of a year ago. 
  • At the beginning of June, the lake-wide average water level of Lake Michigan-Huron was 3 cm (1.2 in) above the seasonal long-term average (1918-2025) and 18 cm (7.1 in) above the level of a year ago.

Forecast outlook in June

  • If weather and water supply conditions are near average, Lake Superior may rise by approximately 7 cm (2.8 in) and Lake Michigan-Huron may increase by approximately 5 cm (2 in). 
  • If conditions are much wetter than average, Lake Superior may increase by approximately 16 cm (6.3 in) and Lake Michigan-Huron may rise by approximately 12 cm (4.7 in).
  • If conditions are much drier than average, the water level of Lake Superior may increase by 1 cm (0.4 in), and Lake Michigan-Huron may decrease by about 1 cm (0.4 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.