Update on Expected Conditions and Upcoming Gate Adjustments on Monday April 24


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 on Monday April 24, 2023. Gates #6 through #16 will each be raised to a setting of 94 cm (37 in.), which is equivalent to approximately five gates fully open.

On Monday, the Rapids flow will increase from 250 m3/s (8,800 cfs) to 770 m3/s (27,100 cfs). At this flow, some low-lying areas of Whitefish Island including recreational trails may flood. Users are encouraged to use extreme caution. The Board advises that even higher flows in the St. Marys Rapids are possible in the coming months, which may increase the level of flooding on Whitefish Island.

The International Lake Superior Board of Control (Board) has been carefully monitoring ice conditions with the goal of raising gates at the Compensating Works as soon as ice conditions permit. The total St. Marys River flow is expected to be 2,160 m3/s (76,300 cfs) in April, which is 250 m3/s (8,800 cfs) less than the flow prescribed by Regulation Plan 2012.

The total flow through the St. Marys River has been lower than what Plan 2012 has prescribed this winter, because of ongoing repairs and maintenance at the hydropower facilities. These repairs and maintenance activities are expected to continue this spring and summer, limiting the amount of flow that can be released through the hydropower facilities. These flow limitations require above-average flows to be released through the Compensating Works at the head of the St. Marys Rapids.

Flows through the St. Marys Rapids in the coming months will depend on weather and water supplies and how much water levels of Lake Superior and Lake Michigan-Huron continue to rise this spring and summer. Recent warm temperatures have quickly melted the snow surrounding Lake Superior and Lake Michigan-Huron. So far in April, Lake Superior has risen by 10 cm and Lake Michigan-Huron has risen by 13 cm. Water levels are expected to continue rising through the spring and into the summer and typically reach a seasonal peak in July or August.

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 or on Facebook at: https://www.facebook.com/InternationalLakeSuperiorBoardOfControl