The International Lake Ontario – St. Lawrence River Board will Temporarily Decrease Outflows through the Moses-Saunders Dam October 8th through 11th


The water level on Lake St. Lawrence at Long Sault Dam on Wednesday morning, October 6th was approximately 72.86 meters (239.04 ft.). The International Lake Ontario-St. Lawrence River Board will temporarily reduce outflows from Lake Ontario from noon on Friday, October 8th through noon on Monday, October 11th to increase water levels on Lake St. Lawrence.  This is intended to provide marinas and shoreline dock owners on Lake St. Lawrence with assistance at the end of the season to remove recreational boats more easily.  Plan prescribed outflows will return at noon on Monday, October 11th.

Lake Ontario outflows will be temporarily reduced by approximately 600 m3/s (21,189 cfs) to reach a target water level of about 73.10 meters (239.83 ft.) on Lake St. Lawrence at Long Sault Dam during the second weekend in October. Water levels on Lake Ontario are expected to be less than one centimeter (0.8 cm) or approximately one third of one inch (0.31 in) higher than they otherwise would be as a result of this action.  There will be a temporary decrease in water levels downstream at Lake St. Louis and Montreal of approximately 30 cm (11.8 in.), which will bring water levels close to the long-term seasonal average. There will be no impact to water levels in Lac Des Deux Montagnes (Lake of Two Mountains) or any locations further upstream along the Ottawa River. “This is a discretionary action that the Board considers pending current and forecast water levels throughout the Lake Ontario-St. Lawrence River system at the end of a given boating season”, said Mr. Steve Durrett, United States Co-Chair of the International Lake Ontario-St. Lawrence River Board.   However, the forecast weather conditions include northeasterly winds which may create less than ideal conditions and may prevent water levels from reaching the target of 73.1 meters (239.83 ft.).  All boaters are encouraged to be mindful of weather conditions and maintain safe boating practices.  

As required by the IJC’s Directive, the small amount of water that will be maintained on Lake Ontario during this temporary flow decrease will be completely offset by an increase in flow later in October. The 4 cm (1.6 in.) of water that was maintained on Lake Ontario during the major (low Criterion H14) deviations (undertaken from May 28 through July 16, 2021) will be retained on Lake Ontario through mid-October.  The discretionary flow reduction is permitted by Plan 2014 and considered a minor deviation. “Lake St. Lawrence was created during the construction of the dam and seaway in the 1950s, and water levels on the lake are directly impacted by regulation outflow and Treaty requirements”, said Mr. David Harper, Canadian Co-Chair of the International Lake Ontario-St. Lawrence River Board.  


Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the Board’s website and posted to the Board’s Facebook page at, and more detailed information is available on its website at


Bryce Carmichael:  (513) 418-8562                    

Sarah Lobrichon:  (613) 794-8592

Or by email :

The International Lake Ontario-St. Lawrence River Board ensures that outflows from Lake Ontario meet the requirements of the International Joint Commission's Orders of Approval. Under any regulation plan, the ability to regulate the outflow from Lake Ontario 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.