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Update on Lake Superior Outflows and Expected Conditions – April 2022


Lake Superior and Lake Michigan-Huron water levels are typically near their seasonal low point at this time of the year. Lake Superior and Lake Michigan-Huron water levels are expected to rise over the coming weeks in response to spring rainfall and snowmelt runoff. Lake Superior water levels remain below the seasonal long-term average while Lake Michigan-Huron 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 1,530 m3/s (54 tcfs) in April, 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 declined 1 cm (0.4 in), which is the average decline in March. Lake Michigan-Huron rose 5 cm (2 in) last month, while on average the lake rises 4 cm (1.6 in) in March. 

At the beginning of April, Lake Superior is 9 cm (3.5 in) below the long-term average water level (1918 – 2021) and 29 cm (11.4 in) below the level of a year ago. Lake Michigan-Huron is 24 cm (9.4 in) above average, 36 cm (14 in) below the level from last year, and 70 cm (28 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 16 cm (6.3 in) and Lake Michigan-Huron water levels may rise by as much as 18 cm (7.1 in) in April.

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: or on Facebook at:

april 2022 infographic lake superior board