During a relatively wet September, Lake Superior rose 4 cm while on average Lake Superior begins its seasonal decline in September. Conditions were closer to average downstream and Lake Michigan-Huron declined 6 cm in September. At the beginning of October, Lake Superior is 17 cm above average (1918 – 2017), but 11 cm below the level at this time last year. Lake Michigan-Huron is currently 43 cm above average, and 2 cm above last year’s beginning-of-October level. The level of Lake Superior is expected to begin its seasonal decline in October, and Lake Michigan-Huron is expected to continue its seasonal decline.

The above-average levels coupled with strong winds and waves continue to result in shoreline erosion and coastal damages across the upper Great Lakes system. Additional shoreline erosion and coastal damages may occur this fall should active weather continue. 

The International Lake Superior Board of Control (Board), under authority granted to it by the International Joint Commission (IJC), has set the Lake Superior outflow to 2,680 cubic metres per second (m3/s) for the month of October, which is as prescribed by 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 of the Compensating Works will be adjusted slightly by raising Gates #9 through #14 to a setting of 97 cm open on Thursday, 4 October; however, with this minimal increase in flow, the gate equivalent will still remain at six gates. Gates #2 through #8, #15 and #16 will be maintained at a setting of 81 cm open. There will be no change to the setting of Gate #1, which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike.

The average St. Marys Rapids flow is expected to be approximately 963 m3/s in October. Anglers and other users of the St. Marys Rapids need to be cautious of the changing flows and water levels that will be experienced in the rapids in October. Furthermore, some flooding of low-lying areas of Whitefish Island is expected to continue this month and some recreational trails and features in these areas will likely be inundated and may sustain damage. Users are encouraged to use extreme caution.                                                                                                                                          

The Board stresses that hydrologic conditions are the primary driver of water level fluctuations. Water levels of the Great Lakes cannot be fully controlled through regulation of outflows, nor can regulation completely eliminate the risk of extreme water levels from occurring during periods of severe weather and water supply conditions. It is not possible to accurately predict such conditions weeks in advance, but given the current levels of the lakes, the Board advises all those that may be impacted to prepare for the above-average water levels, should they continue this summer and fall.


United States
Charles Sidick
(313) 226-3395


Rob Caldwell
(613) 938-5864