Moses-Saunders Dam

IJC’s International Lake Ontario-St. Lawrence River Board announces that better water conditions downstream allow outflows to be set for navigation


Thanks to favorable weather and water supply conditions the board no longer needs to limit outflows to alleviate flooding risks downstream. That means that outflows will now be at the maximum rate to lower water levels on Lake Ontario, while maintaining currents in the St. Lawrence River that allow for commercial navigation.  Water levels throughout the Lake Ontario – St. Lawrence River system are expected to peak well below the record-highs of 2017 and 2019.

Spring 2020 Weather Conditions Show Significant Improvements Over 2019

In the spring, the flows from the Ottawa River basin, a major tributary of the St. Lawrence River, combine with the outflow from Lake Ontario to contribute to the water level of downstream reaches of the St. Lawrence River, near Montreal.  Inflows from Lake Erie, precipitation on the lake and runoff from its drainage basin less any evaporation and the outflow, constrained by downstream conditions, continue to be the factors contributing to the water level of Lake Ontario.

  • The International Lake Ontario – St. Lawrence River Board web page, at, shows the flows in the system.  The Board was able to keep Lake Ontario outflows high because the Ottawa River system reached a lower peak earlier than in 2017 and 2019, In addition, the current flow of the tributary is much lower, as seen in the interactive graphic on the Ottawa River tab. The decline in Ottawa River flow means that conditions downstream are able to handle additional outflow from Lake Ontario.
  • In addition to the recent drier spring conditions in the Lake  Ontario – St. Lawrence River system, the Board has taken every opportunity to remove as much water as possible from Lake Ontario without causing undue impacts upstream and downstream of the Moses-Saunders Power Dam since its peak last June 2019. 

Future Outflow Strategy

The Board may continue to deviate from Plan 2014 as it plans to continue to release as much water as possible while keeping currents at or below safe rates in the critical reaches of the St. Lawrence River.   The IJC granted the board deviation authority last fall, continuing until the peak of Lake Ontario is reached for 2020.

  • The Board, with feedback from mariners, will attempt to release additional outflow than that prescribed in the L-Limits of Plan 2014.    
  • The St. Lawrence Seaway Corporations will undertake measures through its locks and critical reaches of the St. Lawrence River to mitigate the impacts of higher outflows on navigation.
  • In previous years, the Lake Ontario summer outflow reached 10,400 m3/s (367,000 cfs), but with Lake Ontario water levels expected to be lower this year, it is unlikely that this outflow rate will be achieved this year.  With water levels lower, there is less capacity in the channel to move water without an increase in velocity that would impact navigation and recreation and cause detrimental river erosion.
  • Temporary outflow reductions will be required this weekend and possibly again in late-May to allow Hydro-Quebec to safely install several safety booms around their structures prior to summer.  This work was started earlier this spring and would normally be completed during reduced flows for the Ottawa River freshet, but this year outflows have been high and increased more rapidly owing to the Board’s deviation strategy.

Municipalities and residents along the Lake Ontario and St. Lawrence shoreline should continue to discuss and undertake action plans that will build resiliency into the shoreline and prepare for the high and low water events of the future. 

Please note that the Board has created a website page focused on the recent high-water events: (English) [ (French)]. All high-water related materials are now in one easily accessible place. 

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 (English), and more detailed information is available on its website at


Rob Caldwell:              (613) 938-5864                          

Andrew Kornacki:       (716) 879-4349             

The International Lake Ontario – St. Lawrence River Board specifies the outflows from Lake Ontario, according to Plan 2014 as required in the 2016 Supplementary Order from the International Joint Commission. This plan was agreed to by the United States and Canada in December 2016 in an effort to improve environmental performance while maintaining most of the benefits provided to other interests by the previous Plan 1958-D, which was in use since 1963. In determining outflows, the Board, in conjunction with its staff, pays close attention to water levels in the Lake Ontario-St. Lawrence River system and on the Great Lakes upstream, and to the effects on stakeholders within the basin . 

Water levels vary from year-to-year and throughout the year depending on weather and water supply conditions. Such variations benefit coastal wetlands and are critical to a healthy lake environment, but may at times and depending on individual circumstances increase the vulnerability of shoreline structures and reduce opportunities for recreational boating activities. The Board urges everyone to be prepared to live within the full range of levels that have occurred in the past and of those that may occur in the future. Based on historical observations and projected future conditions, at a minimum, Lake Ontario water levels are expected to range from a high of 75.92 m (249.1 ft.) to a low of 73.56 m (241.3 ft.) at infrequent intervals.  However, it is also recognized that future climate conditions are uncertain, and more extreme water levels may be reached and these extremes may occur more often.  Levels on the St. Lawrence River tend to vary more widely than on Lake Ontario. Also, these levels do not include the varying local effects of strong winds and wave action that significantly increase or decrease local water levels on both the lake and river, with temporary changes of over half a meter (two feet) possible in some locations.


For more information, please see the Board’s website ( and Facebook page ( receive a weekly email about water levels and flows in the Lake Ontario–St. Lawrence River system, please send a blank e-mail message to with the word ’subscribe’ in the title and body of your message.