Update on Lake Superior Outflows and Expected Conditions - June 2024
The Board expects the total St. Marys River flow in June to be 2,070 m3/s (73,100 cfs), as 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.
Anglers and other users of the St. Marys Rapids need to be cautious of the changing flows and water levels that will be experienced in the rapids in June. Gate #16 will be opened to a setting of 5 cm on Thursday, June 6 to facilitate sea lamprey trapping. Otherwise, the gate setting of the Compensating Works will be maintained at the current setting (Gates #7 - #14, 100 cm open, equivalent to approximately four gates fully open) through mid-June. To facilitate underwater inspections of the International Bridge piers, gates will be temporarily lowered to a setting equivalent to one-half gate open later this month. A supplementary news release will be issued once inspection dates and gate settings are finalized. Following these inspections, it is expected that the gates will be returned to a setting equivalent to approximately four gates fully open. The average St. Marys Rapids flow in June is expected to be approximately 428 m3/s, to meet the Plan 2012-prescribed flow in June in consideration of the capacity restrictions at the hydropower plants. Gate #1 will remain at its typical setting which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike.
Water level changes over the month of May
Water supply conditions were drier than average in the Lake Superior basin and wetter than average in the Lake Michigan-Huron basin in May.
Lake Superior rose by 7 cm (2.8 in) last month while the seasonal long-term average pattern is for Lake Superior to rise by 10 cm (3.9 in) in May.
Lake Michigan-Huron rose by 10 cm (3.9 in) last month, and the seasonal long-term average pattern is for Lake Michigan-Huron to rise by 8 cm (3.1 in) in May.
Water levels as of the beginning of June
At the beginning of June, the lake-wide average water level of Lake Superior was 5 cm (2.0 in) below the seasonal long-term average (1918-2023) and 31 cm (12.2 in) below the level of a year ago.
At the beginning of June, the lake-wide average water level of Lake Michigan-Huron was 8 cm (3.1 in) above the seasonal long-term average (1918-2023) and 7 cm (2.8 in) below the level of a year ago.
Forecast outlook
Both lakes are expected to continue their seasonal rise over the coming month.
If weather and water supply conditions are near average, Lake Superior may rise by approximately 8 cm (3.1 in.) and Lake Michigan-Huron may rise by approximately 4 cm (1.6 in).
If conditions are much wetter than average, Lake Superior may rise by as much as 16 cm (6.3 in) and Lake Michigan-Huron may rise by as much as 12 cm (4.7 in).
If conditions are much drier than average, the water level of Lake Superior is expected to rise by approximately 1 cm (0.4 in), and Lake Michigan-Huron is expected to decrease by approximately 1 cm (0.4 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