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St. Marys Rapids to see highest flow level since 2019

The flow will increase to approximately 720 cubic meters per second, or 25.4 thousand cubic feet per second
St Marys Rapids stockMP
The St. Mary's River rapids are pictured in this file photo. Michael Purvis/SooToday

Anglers and people using the St. Marys Rapids are advised that the area will see the highest flow since 2019 after June 6.

The compensating works gate movements are scheduled for June 6 and will increase the flow to approximately 720 cubic meters per second, or 25.4 thousand cubic feet per second.

More detailed information about the change is available below in the International Lake Superior Board of Control release. 

Anglers and other users of the St. Marys Rapids, please be advised of the increased flows and water levels that will be experienced in the Rapids in June. After the Compensating Works gate movements scheduled for Monday June 6, the St. Marys Rapids flow is expected to be approximately 720 cubic meters per second (m3/s) (25.4 thousand cubic feet per second (tcfs)) which is the highest flow in the Rapids since 2019.

At these flows, some flooding of low-lying areas of Whitefish Island is expected as additional gates are opened and flows increase. As a result, some recreational trails and features in these areas will likely be flooded, and users are encouraged to use extreme caution.

The water level of Lake Superior rose significantly in May after another month of significantly wetter than average conditions in the basin. Lake Superior increased 22 cm (8.7 in) last month, while on average the lake rises 10 cm (3.9 in) in May. Water supplies were closer to average in the Lake Michigan-Huron basin. Lake Michigan-Huron rose 8 cm (3.2 in) last month, which is the seasonal long-term average for that month. Outflows from Lake Superior and into Lake Michigan-Huron continue to be set in consideration of water levels upstream and downstream.

The Board expects the total outflow to be 2,470 m3/s (87.2 tcfs) in June, which is as prescribed by Lake Superior Regulation Plan 2012. As a result of this increase in total outflow, combined with ongoing repairs at the Canadian hydropower plant, the gate setting at the Compensating Works will be increased to the equivalent of approximately five gates fully open on Monday, June 6. This will be achieved by raising Gates #7 through #12 to a setting of 162 cm (64 in) open. Gate #16 will be opened to a setting 5 cm (2 in) to provide improved efficiency of sea lamprey trapping conducted annually by the U.S. Fish and Wildlife Service.  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.

At the beginning of June, the lake wide water level of Lake Superior is 12 cm (4.7 in) above the seasonal long-term average (1918-2021) and 2 cm (0.8 in) above the level of a year ago. At the beginning of June, the lake-wide level of Lake Michigan-Huron is 27 cm (10.6 in) above average, 14 cm (5.5 in) below the level of a year ago.

Depending on the weather and water supply conditions during the next month, Lake Superior may rise by as much as 15 cm (5.9 in) and Lake Michigan-Huron water levels may rise by as much as 12 cm (4.7 in) in June.