Update on Lake Superior Outflows and Expected Conditions - July 2023
Date

Anglers and other users of the St. Marys Rapids, please be advised that the gate setting of the Compensating Works at the head of the St. Marys Rapids will be maintained at the current setting. Under current hydraulic conditions, the flow in the St. Marys Rapids will be equivalent to that of approximately nine gates fully open. The St. Marys Rapids flow will remain at approximately 1,200 m3/s for the month of July. The International Lake Superior Board of Control (Board) anticipates that flows in the St. Marys Rapids will begin to decrease in August.

Low-lying areas of Whitefish Island including recreational trails are currently flooded and portions of the Island have been closed by Batchewana First Nation. Users are encouraged to use extreme caution.

The Board expects the total St. Marys River flow in July to be 3,050 m3/s (107,700 cfs) which is 20 m3/s (700 cfs) less than the flow prescribed by Regulation Plan 2012. Actual hour-to-hour and day-to-day flows may vary depending on hydrologic conditions, as well as variations in flow from the hydropower plants.

The Board received approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 through November 2023. This deviation strategy is similar to the strategy employed in 2019. Over the next several months, the Board will continue to adjust the gate settings at the Compensating Works in order to offset the flow limitations caused by repairs and maintenance at the hydropower plants. The total amount of water released through the St. Marys River will be approximately equal to the flow prescribed by Plan 2012 and the deviation strategy will have almost no cumulative impact on the water levels of Lake Superior and Lake Michigan-Huron yet will provide reduced fluctuations in flows and water levels in the St. Marys Rapids, directly downstream of the Compensating Works.

Water level changes over the month of June

  • Water supply conditions were much drier than average in both the Lake Superior and Lake Michigan-Huron basins in June.
  • Lake Superior remained stable last month, while the seasonal long-term average pattern is for Lake Superior to rise 7 cm (2.8 in) in June.
  • Lake Michigan-Huron declined by 1 cm (0.4 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to rise 5 cm (2 in) in June.

Water levels as of the end of June

  • At the end of June, the lake-wide average water level of Lake Superior is 19 cm (7.4 in) above the seasonal long-term average (1918-2022) and 8 cm (3.1 in) above the level of a year ago.
  • At the end of June, the lake-wide average water level of Lake Michigan-Huron is 9 cm (3.5 in) above average and 14 cm (5.5 in) below the level of a year ago.

Forecast outlook

The seasonal average pattern is for water levels of Lake Superior and Lake Michigan-Huron to rise in July. On average, Lake Superior and Lake Michigan-Huron reach their seasonal peaks in July or August.

  • If weather and water supply conditions are near average, Lake Superior and Lake Michigan-Huron are expected to rise slightly (~2 cm or 0.8 in) in July.
  • If conditions are wetter than average, Lake Superior may rise by as much as 9 cm (3.5 cm) and Lake Michigan-Huron may rise by as much as 8 cm (3.1 in).
  • If dry conditions continue, water levels of Lake Superior and Lake Michigan-Huron are expected to decline in July.


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