Image of St. Marys River Control Structures

Update on Lake Superior Outflows and Expected Conditions - September 2020


Lake Superior generally remained stable over the course of the month, which is typical for this time of year. Lake Michigan-Huron declined 4 cm (1.6 in) over the course of the month, which is the average water level decline in August.

At the beginning of September, Lake Superior is 6 cm (2.4 in) below the record-high beginning-of-month level set in 1950. The level is currently 26 cm (10.2 in) above average (1918 – 2019). Lake Michigan-Huron is 6 cm (2.4 in) above the previous record-high beginning-of-September level set in 1986. The level is currently 86 cm (33.9 in) above average. 

ILSBC September 2020 Infographic

Water levels are expected to remain high over at least the next few months and further record highs are possible if wet conditions continue. Furthermore, there will continue to be a significantly increased risk of shoreline erosion, lakeshore flooding and coastal damages as high water levels persist. 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.

The Board expects the total outflow to be 2,500 m3/s (88 tcfs) in September, which is as prescribed by Lake Superior Regulation Plan 2012. The outflow in September is just 160 m3/s (5.6 tcfs) above average and the lowest September outflow since 2016, which is in part a reflection of Plan 2012 adjusting to the relatively wetter conditions and higher levels experienced on Lake Michigan-Huron in comparison to Lake Superior in recent months.

On Friday, 4 September, the gate setting of the control structure will be adjusted from the current setting equivalent to approximately two gates open to a setting equivalent to approximately one gate fully open. This will be achieved by lowering Gates #11 through #14 to a setting of 74 cm (29 in) open.

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. The 2020 version of the questionnaire is now available: