Image of St. Marys River Control Structures

Update on Lake Superior Outflows and Expected Conditions - November 2019


Wet weather continued in October, causing Lake Superior water levels to remain relatively stable over the course of the month, while on average the water level declines 3 cm in October.  The monthly mean level in October of 183.88 m is just 3 cm below the record set in 1985, and at the beginning of November, Lake Superior is tied with the record-high beginning-of-month level set in 1985. The level is currently 37 cm above average (1918 – 2018) and 9 cm above its level of a year ago.

Lake Michigan-Huron also remained relatively stable over the course of October, while on average the water level declines 7 cm in October. Lake Michigan-Huron is currently 17 cm below the record-high beginning-of-month level set in 1986. The level is 90 cm above average, and 42 cm above last year’s beginning-of-November level.  

Lake Superior and Lake Michigan-Huron are expected to resume their seasonal declines in November, but will remain near record-highs for this time of year. As a result, there will continue to be a significantly increased risk of shoreline erosion, lakeshore flooding and coastal damages over the next several weeks and potentially through the fall. 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 from Lake Superior to be 2,820 m3/s in November, which is as prescribed by Lake Superior Regulation Plan 2012.  Actual outflows may vary depending on hydrologic conditions, as well as maintenance activities at the hydropower plants on the St. Marys River. The gate setting at the Compensating Works will be maintained at the equivalent of six gates fully open to start the month. The gate setting will then be lowered in stages beginning in late November to allow for a gradual reduction in St. Marys Rapids flows and water levels prior to winter.

The average St. Marys Rapids flow in November is expected to be approximately 937 m3/s. Anglers and other users of the St. Marys Rapids need to be cautious of the high flows and water levels that will continue to be experienced in the rapids in November. Furthermore, some flooding of low-lying areas of Whitefish Island is expected to continue at these high flows. As a result, some recreational trails and features in these areas will likely be inundated and may sustain damage. Users are encouraged to use extreme caution.