Update on Lake Superior Outflows and Expected Conditions - November 2023
Date

The gate setting of the Compensating Works at the head of the St. Marys Rapids will be lowered in November to a
setting equivalent to approximately one gate fully open. After the gate adjustments on Monday, November 6 (U.S.
gates) and Tuesday, November 7 (Canadian gates), the St. Marys Rapids flow will be approximately 150 m3/s.


The Board expects the total St. Marys River flow in November to be 2,300 m3/s (81,200 ft3/s), as prescribed by
Regulation Plan 2012. Actual hour-to-hour and day-to-day flows may vary depending on hydrologic conditions, as
well as variations in flow from the hydropower plants.

Water level changes over the month of October
Water supply conditions were very dry in the Lake Superior basin and very wet in the Lake Michigan-Huron basin in
October.

  • Lake Superior declined by 10 cm (3.9 in) last month, while the seasonal long-term average pattern is for Lake Superior to decline by 4 cm (1.6 in) in October.
  • Lake Michigan-Huron declined by 4 cm (1.6 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to decline by 7 cm (2.8 in) in October.

Water levels as of the beginning of November

  •  At the beginning of November, the lake-wide average water level of Lake Superior was the same as the seasonal long-term average (1918-2022) and 7 cm (2.8 in) below the level of a year ago.
  • At the beginning of November, the lake-wide average water level of Lake Michigan-Huron was 14 cm (5.5 in) above the seasonal long-term average (1918-2022) and 2 cm (0.8 in) below the level of a year ago.

Forecast outlook
Both Lakes Superior and Michigan-Huron are in their seasonal decline.

  • If weather and water supply conditions are near average, both Lake Superior and Lake Michigan-Huron are expected to decline in November (by 6 cm (2.4 in) and 5 cm (2 in), respectively).
  • If conditions are wetter than average, both Lake Superior and Lake Michigan-Huron may rise slightly (by 1 cm (0.4 in) and 3 cm (1.2 in) respectively).
  • If conditions are drier than average, the water level of Lake Superior is expected to decline by as much as 11 cm (4.3 in.), and Lake Michigan-Huron is expected to decline by as much as 12 cm (4.7 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