Updated Gate Changes, Outflows, and Expected Conditions – August 2025
Anglers and other users of the St. Marys Rapids, please be advised that the gates of the Compensating Works at the head of the St. Marys Rapids will be adjusted multiple times in August to facilitate underwater inspections and scour surveys and to meet the Plan 2012-prescribed flow in consideration of capacity restrictions at the hydropower plants. Please note that as the gates are adjusted, outflows through the St. Marys River will fluctuate. Low-lying areas of Whitefish Island including recreational trails may flood as the gates are increased in August. Please take extra caution when recreating and navigating the river and adjacent areas.
Gate changes
As reported in the news release issued August 1, the current gate setting is equivalent to two gates fully open (Gate #1 open 20 cm (8 in), Gate #10 open 71 cm (28 in), and Gates #11 through #14 open 79 cm (31 in). Gate #1 is set to 20 cm (8 in) open as of August 7, 2025.
The inspection of Gates #1 through #8 was successful. Minor adjustments to gate settings resulting from the inspection are necessary. Gate #5 will remain closed for the rest of August. The table below shows the updated gate movements that will take place the remainder of the month and the associated outflows.
| Date | Action | St. Marys Rapids Flow |
| August 8 | Gate #9 through #14 will be raised to 102 cm (40 in) and Gate #16 will be closed. | 451 m3/s (equivalent to 3 gates fully open) |
| August 11 | Gates #2 through #4 and #6 through #8 will be raised to 102 cm (40 in) | 886 m3/s (equivalent to 6 gates fully open) |
| August 18 | To facilitate scour surveys on August 19 and 20, Gates #2 through #4 and #6 will be lowered to 20 cm (8 in) open and Gates #7 through #14 will be closed. | 88 m3/s (equivalent to one-half gate fully open) |
| August 21 | Gates #2 through #14, except Gate #5, will be raised to 102 cm (40 in) | 886 m3/s (equivalent to 6 gates fully open) |
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 from occurring during periods of severe weather and water supply conditions. Additional information can be found at the Board’s homepage: https://ijc.org/en/lsbc.