aerial view st marys

Update on Lake Superior Outflows and Expected Conditions


Anglers and other users of the St. Marys Rapids are advised that Gate #16, which is the southernmost gate of the Compensating Works structure, located closest to the U.S. shoreline at the head of the rapids, will be temporarily opened beginning on Thursday, June 17th to a setting of 5 cm (2 in). This small, concentrated increase will help facilitate the sea lamprey trapping program conducted annually by the U.S. Fish and Wildlife Services. The gate will remain at this setting through July and will be closed at the start of August 2021.

This slight adjustment in gate setting will have no measurable effect on total outflow.


The International Lake Superior Board of Control is responsible for regulating the outflow of Lake Superior and managing the control works on the St. Marys River. Under any regulation plan, the ability to regulate the outflow from Lake Superior does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes, precipitation, evaporation, and runoff cannot be controlled, and are difficult to accurately predict. Outflow management cannot eliminate the risk of extreme water levels from occurring during periods of severe weather and water supply conditions. Additional information can be found at the Board’s homepage: or on Facebook at: