Third Consecutive Month of Record Outflows: continued risk of high water on the St. Lawrence River and on Lake Ontario


Due to favorable ice conditions and previously implemented deviation strategies, the Lake Ontario outflows surpassed the historical record-high for the month of March, making this the third straight monthly record that has been exceeded during the Board’s ongoing efforts to deviate from Plan 2014 and remove water from Lake Ontario.

The International Lake Ontario–St. Lawrence River Board met Friday, 27 March to review conditions and assess the previously announced strategy for maximizing outflows to remove water from Lake Ontario.

Outflows above the Plan 2014 F Limit have been released over the past three weeks.  The F Limit, also known as the “flood” limit, is meant to balance high water impacts upstream and downstream, typically during the spring when wet weather, snow melt and rising Ottawa River flows tend to cause levels to rise throughout the Lake Ontario – St. Lawrence River system.  The Board proactively targeted a level of 22.20 m (72.8 ft) in recent weeks, 10 cm (4 in) higher than what would normally apply under Plan 2014 given recent Lake Ontario levels.  This allowed several centimeters of additional water to be removed from Lake Ontario in advance of the expected Ottawa River freshet, which combined with Lake Ontario outflows, also increases flows and water levels in the lower St. Lawrence River at this time of year. 

Starting 1 April, higher levels at Lake St. Louis will be targeted.  Outflows will be set to allow Lake St. Louis to reach 22.33 m (73.3 ft), which normally applies only when levels of Lake Ontario are between 75.37 m (240.7 ft) m and 75.5 m (247.7 ft).  Lake Ontario is at 75.24 m (246.8 ft) as of 31 March and continues to rise gradually.  The Board agreed to this strategy after considering the high likelihood that a level of 22.33 m will be reached in the coming weeks even without deviating, and that targeting this level sooner will allow slightly more water to be removed from Lake Ontario in advance, which may reduce the risk of higher levels both upstream and downstream later this spring.

The Board’s strategy will also consider conditions further downstream on the St. Lawrence River at Lake St. Peter.  Like Lake Ontario, this area of the St. Lawrence River also suffered severe flooding impacts during the springs of 2017 and 2019, and while uncertain at this time, there remains a risk it will see similar impacts this year.  If the Lake St. Peter gauge is expected, within 24 hours, to rise and remain 2.7 m (8.8 ft) or more above chart datum, then outflows will be adjusted to follow the applicable tier of the F Limit according to the level of Lake Ontario.

The Board has also considered the effects of high Lake Ontario outflows on commercial navigation in the St. Lawrence River.  Cross-currents at critical reaches of the Seaway may also limit the outflow, depending on levels in the lower St. Lawrence River and the threat of flooding in these areas.  As of 1 April, in coordination with commercial navigation experts and mariners, the Board has agreed to increase outflows as quickly and as much as possible above the Plan 2014 safe navigation limit (L Limit). 

The additional water removed from Lake Ontario due to deviations from both the F and L limits will likely be on the order of a few centimeters, or a couple inches, and therefore, small in comparison to what is already being removed by the rules of Plan 2014, and also in comparison to the seasonal increase of water supplies into the Ontario basin.  Nonetheless, the Board also recognizes the importance of removing any additional water it can during this critical spring period. 

The Board continues to monitor conditions and flows around Lake Ontario, the lower St. Lawrence River, and in the Ottawa River basin, and will continue to consider further adjustments to its strategies over the next several weeks.  Updated information on current and expected conditions on the Ottawa River can be found on the Ottawa River Regulation Planning Board’s website here:

While the COVID-19 pandemic situation continues to change rapidly, the Board remains committed to ensuring it continues to regulate the outflow from Lake Ontario, communicate its evolving strategy and its impacts to all interests in the system while the COVID-19 pandemic unfolds.  Media, local officials and members of the public may still communicate with the Board’s Secretaries using the ‘Contact’ form on the website.

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.