Image of St. Marys River Control Structures

Update on Lake Superior Outflows and Expected Conditions - June 2021


Lake Superior and Lake Michigan-Huron water levels are above their respective long-term averages. Therefore, there is a risk of shoreline erosion, lakeshore flooding, and coastal damages.  The International Lake Superior Board of Control (Board) advises shoreline businesses and property owners to prepare for potentially severe coastal impacts during periods of strong winds and high waves. Lake Superior outflows are set in consideration of the above-average levels upstream and downstream.

The Board expects the total outflow to be 2,280 m3/s (80.5 tcfs) in June, which is as prescribed by Lake Superior Regulation Plan 2012. On Monday, June 7, the gate setting of the control structure will be decreased from the setting equivalent to approximately three gates fully open to a setting equivalent to approximately one gate fully open. This will be achieved by lowering Gates #9 through #12. Anglers and other users of the St Marys Rapids need to be cautious of changing flows and water levels.

ILSBC June 2021 Infographic - English

Weather and water supply conditions were very dry throughout the entire Great Lakes basin in May. As a result, Lake Superior remained stable last month, while on average the lake rises 10 cm in May. Lake Michigan-Huron also remained stable, for the third month in a row. Historically, Lake Michigan-Huron rises an average 8 cm (3.2 in) in May. At the beginning of June, Lake Superior is 10 cm (3.9 in) above average (1918 – 2020), 15 cm (5.9 in) below the level of a year ago, and 30 cm (11.8 in) below the record-high level at this time in 2019. Lake Michigan-Huron is 41 cm (16.1 in) above average and 50 cm (19.7 in) below the record-high level at this time last year.

Lake Superior and Lake Michigan-Huron water levels typically rise in June.  Depending on the weather and water supply conditions during the next month, Lake Superior may remain stable or may rise by up to approximately 15 cm (5.9 in) in June. Lake Michigan-Huron may decline slightly or may rise by up to approximately 10 cm (3.9 in) in June.

Shoreline businesses and property owners are reminded that the Great Lakes – St. Lawrence River Adaptive Management (GLAM) Committee continues to host an online questionnaire to allow for direct reporting on impacts related to high water conditions:  


The International Lake Superior Board of Control is responsible for regulating the outflow of Lake Superior and managing the control works on the St. Marys River. Under any regulation plan, the ability to regulate the outflow from Lake Superior does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes, 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: or on Facebook at: