Image of St. Marys River Control Structures

Update on Lake Superior Outflows and Expected Conditions - March 2021


Lake Superior and Lake Michigan-Huron water levels continue to decline, but are still well above average and the risk of high-water impacts remains.  Lake Superior outflows continue to be set in consideration of high levels upstream and downstream.

Last month, Lake Superior declined 4 cm (1.6 in), while on average it declines 5 cm (2.0 in) in February. Lake Michigan-Huron declined 4 cm (1.6 in) over the course of the month, while on average it declines 1 cm (0.4 in) in February.  

Both lakes are expected to continue their seasonal declines in March. However, there will continue to be an increased risk of shoreline erosion, lakeshore flooding and coastal damages over the next several weeks and potentially through the spring. The International Lake Superior Board of Control (Board) advises all those that may be affected to prepare for potentially severe coastal impacts, especially during periods of strong winds and high waves.

ILSBC March 2021 Infographic

At the beginning of March, Lake Superior is 19 cm (7.5 in) above average (1918 – 2020), 14 cm (5.5 in) below its level of a year ago, and 18 cm (7.1 in) below its record-high level of 1986. Lake Michigan-Huron is 67 cm (26.4 in) above average and 26 cm (10.2 in) below the record-high level at this time last year.

The Board expects the total outflow to be 2,040 m3/s (72 tcfs) in March, which is as prescribed by Lake Superior Regulation Plan 2012. The gate setting of the control structure will be maintained at the typical winter setting equivalent to one-half gate open in March.

Shoreline businesses and property owners are reminded that the Great Lakes – St. Lawrence River Adaptive Management (GLAM) Committee continues to host an online questionnaire to allow for direct reporting on impacts related to recent high water conditions: