Update on Upcoming Gate Changes, Outflows and Expected Conditions – November 2025
Date

The Board expects the total St. Marys River flow in November to be 2,330 m3/s (82,300 ft3/s) as prescribed by Regulation Plan 2012.

The gate setting of the Compensating Works at the head of the St. Marys Rapids will be lowered this month. The St. Marys Rapids flow will decrease from approximately 308 m3/s or 10,900 ft 3/s (equivalent to approximately two gates fully open) to approximately 87 m3/s or 3,100 ft3/s (equivalent to approximately one-half gate open). On Thursday, November 6, Gate #9 and #10 will be lowered to a setting of 20 cm (8 in), and Gate #11 will be closed. Gates #7 and #8 will remain at their current setting of 20 cm (8 in.). Gate #1 will remain at its setting which supplies a flow of about 15 m3/s (500 ft3/s) to the channel north of the Fishery Remedial Dike. 

Water level changes over the month of October

Water supply conditions were drier than average in the Lake Superior basin and much drier than average in the Lake Michigan-Huron basin in October.

  • Lake Superior decreased by 6 cm (2.4 in) last month, while the seasonal long-term average pattern is for Lake Superior to decline by 3 cm (1.2 in) in October.
  • Lake Michigan-Huron declined by 12 cm (4.7 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to decline by 7 cm (2.8 in) in October.

Water levels as of the end of October

  • At the end of October, the lake-wide average water level of Lake Superior was 8 cm (3.1 in) below the seasonal long-term average (1918-2024) and 11 cm (4.3 in) above the level of a year ago.
  • At the end of October, the lake-wide average water level of Lake Michigan-Huron was 22 cm (8.7 in) below the seasonal long-term average (1918-2024) and 15 cm (5.9 in) below the level of a year ago.

Forecast outlook

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