Update on Lake Superior Outflows and Expected Conditions - August 2022


Anglers and other users of the St. Marys Rapids, please be advised that the St. Marys Rapids flows and water levels will increase in August. As of Friday, August 5, the St. Marys Rapids flow is expected to be approximately 923 cubic meters per second (m3/s) (32.6 thousand cubic feet per second (tcfs)). At these flows, some flooding of low-lying areas including recreation trails on Whitefish Island is expected, and everyone is 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 2,660 m3/s (93.9 tcfs) in August, which is as prescribed by Lake Superior Regulation Plan 2012. Compensating Works Gates #13 and #14 will be raised to a setting of 97 cm (39 in) open on Friday, August 5. Gate #16 will be closed now that sea lamprey trapping has been completed for the season.  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. Note that Gates #9 through #12 were adjusted on July 12 instead of July 6 as originally scheduled and posted in the July 1 news release. Gates #7 and #8 were raised as scheduled on July 6.

Water supplies were near average in the Lake Superior basin in July. Lake Superior rose 4 cm (1.6 in) last month, which is near the seasonal long-term average rise in July of 5 cm (2 in). Water supplies were drier than average in the Lake Michigan-Huron basin in July. As a result, Lake Michigan-Huron declined 2 cm (0.8 in) last month, while on average the lake remains stable in July.

At the beginning of August, the lake-wide water level of Lake Superior is 10 cm (3.9 in) above the seasonal long-term average (1918-2021) and 7 cm (2.8 in) above the level of a year ago. At beginning of August, the lake-wide level of Lake Michigan-Huron is 21 cm (8.3 in) above average, 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 by as much as 8 cm (3.1 in) in August, or may begin its seasonal decline. Lake Michigan-Huron water levels may rise slightly in August or may decline by as much as 10 cm (3.9 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