Update on Lake Superior Outflows and Expected Conditions - September 2022


Anglers and other users of the St. Marys Rapids, please be advised that the St. Marys Rapids flows and water levels will increase slightly in September. As of Wednesday, September 7, the St. Marys Rapids flow is expected to be approximately 931 cubic metres per second (m3/s) (32.9 thousand cubic feet per second (tcfs)).  At these flows, some flooding of low-lying areas of Whitefish Island is expected. As a result, some recreational trails and features in these areas will likely be flooded, and users are encouraged to use extreme caution.

Outflows from Lake Superior and into Lake Michigan-Huron continue to be set in consideration of water levels upstream and downstream. The Board expects the total outflow to be 2,670 m3/s (94.3 tcfs) in September, which is as prescribed by Lake Superior Regulation Plan 2012. Compensating Works Gates #13 and #14 will be raised to a setting of 104 cm (41 in.) open on Wednesday, September 7. 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.

Lake Superior rose 1 cm (0.4 in) last month, which is the seasonal long-term average rise in August. Lake Michigan-Huron declined 4 cm (1.6 in) last month, which is the seasonal long-term average decline in August.

At the beginning of September, the lake-wide water level of Lake Superior is 10 cm (3.9 in) above the seasonal long-term average (1918-2021) and 11 cm (4.3 in) above the level of a year ago. At the beginning of September, the lake-wide level of Lake Michigan-Huron is 21 cm (8.3 in) above average and 24 cm (9.5 in) below the level of a year ago.

Depending on the weather and water supply conditions during the next month, Lake Superior may rise by as much as 7 cm (2.8 in) in September, or may begin the seasonal decline. Lake Michigan-Huron water levels may rise slightly in September or may decline by as much as 12 cm (4.7 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