Update on Lake Superior Outflows and Expected Conditions - July 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 July. As of Wednesday July 6, the St. Marys Rapids flow is expected to be approximately 786 cubic
meters per second (m 3 /s) (27.8 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 2,650 m 3 /s (93.6 tcfs) in July, which is prescribed
by Lake Superior Regulation Plan 2012. Compensating Works Gates #7 through #12 will be raised to a setting of 175
cm (69 in) open on Wednesday, July 6. Gate #16 will remain partially opened to a setting of 5 cm (2 in) to provide
improved efficiency of sea lamprey trapping conducted annually by the U.S. Fish and Wildlife Service. There will be
no change to the setting of Gate #1, which supplies a flow of about 15 m 3 /s to the channel north of the Fishery
Water supplies were near average in the Lake Superior basin in June. Lake Superior rose 7 cm (2.8 in) last month,
which is the seasonal long-term average rise in June. Water supplies were drier than average in the Lake Michigan-
Huron basin in June. As a result, Lake Michigan-Huron rose 2 cm (0.8 in) last month, while on average the lake rises 6
cm (2.4 in) in June.
At the end of June, the lake-wide water level of Lake Superior is 12 cm (4.7 in) above the seasonal long-term average
(1918-2021) and 3 cm (1.2 in) above the level of a year ago. At the end of June, the lake-wide level of Lake Michigan-
Huron is 23 cm (9.1 in) above average, 16 cm (6.3 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
10 cm (3.9 in) or may begin the seasonal decline. Lake Michigan-Huron water levels may rise by as much as 7 cm
(2.8 in) in July or may begin the seasonal decline.
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