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Update on Lake Superior Outflows and Expected Conditions - July 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 2,370 m3/s (83.7 tcfs) in July, which is as prescribed by Lake Superior Regulation Plan 2012. On Tuesday, July 6th, the gate setting of the control structure will be decreased from the setting equivalent to one gate open to a setting equivalent to approximately one-half gate fully open by adjusting Gates #9 through #12. Anglers and other users of the St Marys Rapids need to be cautious of changing flows and water levels.

ILSBC July 2021 Infographic

Weather and water supply conditions were dry again in June. As a result, Lake Superior rose 5 cm (2 in), while on average the lake rises 7 cm (3 in) in June. Lake Michigan-Huron rose 3 cm (1.2 in) last month. Historically, Lake Michigan-Huron rises an average of 5 cm (2 in) in June. At the beginning of July, Lake Superior is 8 cm (3.2 in) above average (1918 – 2020), 16 cm (6.3 in) below the level of a year ago, and 28 cm (11 in) below the record-high level at this time in 2019. Lake Michigan-Huron is 39 cm (15.4 in) above average and 49 cm (19.3 in) below the record-high level set at this time last year.

Lake Superior and Lake Michigan-Huron water levels typically rise in July. Depending on the weather and water supply conditions during the next month, Lake Superior may decline slightly or may rise by up to approximately 10 cm (3.9 in) in July. Lake Michigan-Huron may decline slightly or may rise by up to approximately 5 cm (2 in) in July.

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: