Water Levels on Lake St. Lawrence to be Temporarily Increased October 7th through 10th, While Water Levels on Lake St. Louis to be Temporarily Decreased


The International Lake Ontario-St. Lawrence River Board will temporarily reduce outflows from Lake Ontario at the Moses Saunders Dam from noon on Friday, October 7th through noon on Monday, October 10th to reach a target water level of about 73.10 meters (239.83 ft.) on Lake St. Lawrence at Long Sault Dam. 

This temporary increase in water levels on Lake St. Lawrence is intended to help people remove recreational boats more easily as the season ends.  After the flow reduction is complete at noon on Monday, October 10th, water levels will decrease once again on Lake St. Lawrence. For those needing higher levels to remove their boats, this holiday weekend will be the only opportunity.

Over the long term, Lake St. Lawrence water levels are influenced by water supplies, Lake Ontario water levels, and outflows from Lake Ontario into the St. Lawrence River. ‘The Board recognizes that water levels experienced throughout the Lake Ontario-St. Lawrence River system vary significantly depending on location but nowhere are fluctuating water levels so inescapable as experienced on Lake St. Lawrence,’ said General Peeples, United States Co-Chair of the International Lake Ontario-St. Lawrence River Board.  Water levels have been near record lows for much of the recreational boating season since early July.

Changes in wind speed and direction also have a significant influence on the water levels of Lake St. Lawrence on an hourly and daily basis. The daily mean water level has fluctuated a lot in recent weeks, from 72.86 metres (239.04 feet) on September 27th to 72.49 metres (237.82 feet) on October 2nd, a decline of 37 cm (14.6 inches) because of sustained northeast wind.  Fortunately, a southwest wind is forecast for this weekend.

Lake St. Lawrence is a man-made widening in the St. Lawrence River that was constructed to manage the Moses-Saunders Dam.  Good recreational boating conditions were not a primary design use of the Moses Saunders Dam and therefore cannot be guaranteed every season,’ said Mr. David Harper, Canadian Co-Chair of the International Lake Ontario-St. Lawrence River Board.  All boaters are encouraged to be mindful of weather conditions, maintain safe boating practices, and be prepared to adapt to the full range of water levels that have been observed historically.    

There will be a temporary decrease in water levels downstream at Lake St. Louis and Montreal of approximately 30 cm (11.8 in.) over the weekend. There will be no impact to water levels in Deux-Montagnes Lake or any locations further upstream along the Ottawa River.

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 the reduced outflows. 

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 in the coming months as conditions permit. The discretionary flow reduction is permitted by Plan 2014 and considered a minor deviation. 

Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the Board’s website at https://www.ijc.org/en/loslrb and posted to the Board’s Facebook page at https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard.





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.