Image of St. Marys River Control Structures

Update on Lake Superior Outflow and Expected Conditions - March 2019


Very wet conditions continued across the upper Great Lakes basin in February, and water levels of Lake Superior and Lake Michigan-Huron remain well above average. 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 winter should active weather continue. 

Lake Superior water levels remained stable last month while on average the level declines 5 cm in February. At the beginning of March, Lake Superior is 34 cm above average (1918 – 2017) and equal to the level at this time last year. Lake Superior is expected to remain relatively stable or decline slightly during the coming month. Lake Michigan-Huron rose 4 cm, while on average it declines 1 cm in February. Lake Michigan-Huron is currently 57 cm above average, and 6 cm above last year’s beginning-of-March level.  Lake Michigan-Huron is expected to continue its seasonal rise in March.

In consideration of the continuing high water levels in the upper Great Lakes and to accommodate expected maintenance at the hydropower plants, the International Lake Superior Board of Control (Board) requested and received approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 this winter. All three hydropower plants will continue to be directed to flow at their maximum available capacity, but the total combined available capacity was less than normal in December and January due to required maintenance activities. To offset the effects of these activities, over the winter months the Board will release more water through the control structure at the head of the St. Marys Rapids by maintaining a gate setting equivalent to two gates fully open instead of the typical winter setting equivalent to one-half gate open.    

The net result of this strategy is that total flows were less than Plan 2012 in December and January, while flows greater than Plan 2012 occurred in February and are expected again in March.  The total amount of water released through the St. Marys River this winter will be approximately equal to releases called for by Plan 2012, and the net effects on the water levels of Lake Superior and Lake Michigan-Huron are expected to be minimal by spring.

The Board expects the total flow in March to be 2,580 m3/s, which is 170 m3/s more than that prescribed by Plan 2012. Actual outflows may vary depending on hydrologic and ice conditions, as well as maintenance activities at the hydropower plants on the St. Marys River.  The gate setting of the control structure will be maintained at the current setting (Gates #2 through #16 open 26 cm each) which is equivalent to two gates fully 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 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 winter.