Update on Lake Superior Outflows and Expected Conditions – May 2022


In response to wet weather in April, the water level of Lake Superior has risen and reached the long-term average value for the beginning of May. The lake-wide water level of Lake Michigan-Huron also rose in April and remains above the seasonal long-term average. 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 1,910 m3/s (67 tcfs) in May, 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 (7.9 in)). 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 increased 14 cm (5.5 in), while on average the lake rises 8 cm (3.2 in) in April. Lake Michigan-Huron rose 13 cm (5.1 in) last month, while on average the lake rises 11 cm (4.3 in) in April.

At the beginning of May, the water level of Lake Superior is equivalent to the long-term average water level (1918 – 2021) and 18 cm (7.1 in) below the level of a year ago. Lake Michigan-Huron is 27 cm (10.6 in) above average, 22 cm (8.7 in) below the level from last year, and 62 cm (24.4 in) below the record-high level set at this time in 2020.

Depending on the weather and water supply conditions during the next month, Lake Superior may rise by as much as 19 cm (7.53 in) and Lake Michigan-Huron water levels may rise by as much as 16 cm (6.3 in) in May.

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