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

Anglers and other users of the St. Marys Rapids, please be advised that a higher than customary gate setting continues to be maintained to minimize the impacts of ongoing maintenance at Evolugen’s Clergue hydropower facility in Canada. The gates of the Compensating Works at the head of the St. Marys Rapids will be maintained at an equivalent of two gates fully open (Gates #6 through #16 partially open 26 cm (10 in) each) for the start of April. The International Lake Superior Board of Control (Board) is 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 will be 2,040 m3/s (72.0 tcfs) for the start of April, which is 370 m3/s (13.1 tcfs) less than the flow prescribed by Regulation Plan 2012. The Board will issue another notice in advance of gate movements planned for later this month.


Water level changes over the month of March
 Lake Superior declined by 4 cm (1.4 in) last month, while the seasonal long-term average decline is 1 cm (0.4 in) in March.
 Lake Michigan-Huron rose by 4 cm (1.6 in) last month, which is the seasonal long-term average rise in March.


Water levels as of the beginning of April
 At the beginning of April, the lake-wide water level of Lake Superior is 18 cm (7.1 in) above the seasonal long-term average (1918-2021) and 24 cm (9.4 in) above the level of a year ago.
 At the beginning of April, the lake-wide level of Lake Michigan-Huron is 11 cm (4.3 in) above average and 14 cm (5.5 in) below the level of a year ago.


Forecast outlook
 Depending on the weather and water supply conditions during the next month, Lake Superior may decline slightly in April, or it may rise by as much as 14 cm (5.5 cm).
 Depending on the weather and water supply conditions, Lake Michigan-Huron is expected to continue its seasonal rise in April and may rise by as much as 20 cm (7.9 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 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