Update on Lake Superior Outflows and Expected Conditions - October 2021


Lake Superior and Lake Michigan-Huron have both continued their seasonal declines in September. As a result of the drier than average conditions, water levels on Lake Superior have gone below the seasonal long-term average for the first time since April 2014. Lake Michigan-Huron water levels have declined significantly from the record-high levels observed in recent years, but water levels remain above the seasonal long-term average. Lake Superior outflows continue to be set in consideration of water levels upstream and downstream.

The Board expects the total outflow to be 2,030 m3/s (74.5 tcfs) in October, which is as prescribed by Lake Superior Regulation Plan 2012. The gate setting at the Compensating Works will be maintained at the setting equivalent to one-half gate open (Gates #7 through #10 partially open 20 cm). There will be no change to the setting of Gate #1, which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike.

Weather and water supply conditions were drier than average on both Lake Superior and on Lake Michigan-Huron in September. As a result, Lake Superior declined 5 cm (2.0 in), while on average the lake declines 2 cm (0.8 in) in September. Lake Michigan-Huron declined 14 cm (5.5 in) last month, while the average historical decline is 6 cm (2.4 in) in September. At the beginning of October, Lake Superior is 4 cm (1.6 in) below the long-term average water level (1918 – 2020) and 31 cm (12.2 in) below the level of a year ago. Lake Michigan-Huron is 39 cm (15.4 in) above average 42 cm (16.5) below the level from last year, and 61 cm (24 in) below the record level set in 1986.

Lake Superior and Lake Michigan-Huron water levels typically decline in October. Depending on the weather and water supply conditions during the next month, Lake Superior may decline by as much as 7 cm (2.8 in) in October. Lake Michigan-Huron water levels could decline by as much as 15 cm (5.9 in).
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: https://ijc.org/glam/questionnaire.

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: https://ijc.org/en/lsbc or on Facebook at: https://www.facebook.com/InternationalLakeSuperiorBoardOfControl