Update on Lake Superior Outflows and Expected Conditions - October 2022


Anglers and other users of the St. Marys Rapids, please be advised that the St. Marys Rapids flows and water levels will remain above average in October. Compensating Works Gates #7 through #12 will remain at a setting of 175 cm (69 in) open and Gates #13 and #14 will remain at a setting of 104 cm (41 in) open. 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. The flow through the rapids is expected to be approximately 933 cubic meters 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. Due to ongoing maintenance at the Canadian hydropower facility, the International Lake Superior Board of Control (Board) anticipates that St. Marys River flows will be below those prescribed by Regulation Plan 2012 this winter. To offset this, a flow of 2,730 m3/s, which is 70 m3/s higher than the flow prescribed by Plan 2012, will be released in October.

As of the beginning of October, Lake Superior is at the same water level as the beginning of September. On average, the lake declines 2 cm in September. Lake Michigan-Huron declined 10 cm (3.9 in) last month, while the seasonal long-term average decline in September is 6 cm (2.4 in).

At the beginning October, the lake-wide water level of Lake Superior is 11 cm (4.3 in) above the seasonal long-term average (1918-2021) and 15 cm (5.9 in) above the level of a year ago. At the beginning of October, the lake-wide level of Lake Michigan-Huron is 17 cm (6.7 in) above average and 22 cm (8.7 in) below the level of a year ago.

Depending on the weather and water supply conditions during the next month, Lake Superior may rise slightly in October, or may begin the seasonal decline. The water level of Lake Michigan-Huron is expected to continue the seasonal decline and may decline by as much as 14 cm (5.5 in) in October.

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