Moses-Saunders Dam

Additional outflow strategies to address high water levels on Lake Ontario and the St. Lawrence River


The International Lake Ontario–St. Lawrence River Board agreed March 11th to amend its Plan 2014 temporary deviation strategies to allow for additional increases to the rate of water removed from Lake Ontario through the spring.

The first adjustment to the deviation strategy involves the Plan 2014 rule that attempts to balance high water impacts upstream and downstream of the Moses-Saunders Power Dam known as the Flood Limit (F Limit).  When applicable, outflows are adjusted to maintain corresponding levels upstream and downstream. For example, when Lake Ontario is below 75.30 m (247.05 ft) outflows can be adjusted to bring Lake St. Louis up to its flood alert level of 22.10 m (75.51 ft).

While Lake Ontario remains below 75.30 m (247.05 ft) currently, the Board expects Lake Ontario to rise through spring.  The Board is proactively increasing outflows to target downstream levels to 22.20 m (72.80 ft) or more, in anticipation of Lake Ontario eventually reaching 75.30 m (247.05 ft).  Please note, water levels may at times rise above this level by several centimeters, particularly during periods of rapid snow melt and heavy rains in southern parts of the southern part of the Ottawa River basin and around the Montreal area. The Board is also considering further increases at Lake St. Louis, which may be necessary should Lake Ontario continue rising.

The second deviation strategy amendment will begin April 1st, following the opening of the St. Lawrence Seaway.  Working closely with commercial navigation experts, outflows will be increased as quickly and as much as possible above the Plan 2014 usual safe navigation limit (L Limit).  This strategy will be implemented to ensure that the maximum possible outflows are maintained while allowing for safe navigation to continue. The Board notes that other considerations may take precedence and limit outflows, including Ottawa River flows and water levels in the lower St. Lawrence River. 

The Board continues monitoring conditions throughout the system, including the effects of high outflows on lower St. Lawrence River water levels in order to continue maximizing outflows from Lake Ontario as much as possible.

Lake Ontario’s seasonal rise has begun, and will generally continue in the coming weeks.  Residents and communities along Lake Ontario should remain vigilant and continue to make preparations for potential impacts of high water this spring, as the risk remains elevated, particularly during periods of strong winds and waves. 

There remains considerable long-term uncertainty for peak levels that will be reached this season, both upstream on Lake Ontario and downstream in the lower St. Lawrence River.  Water levels will largely be determined by precipitation, inflows from Lake Erie and from the Ottawa River system over the next several weeks.  Updated information on current conditions on the Ottawa River can be found on the Ottawa River Regulation Planning Board’s website here:

Residents along the St. Lawrence River should be aware that water levels could fluctuate significantly during this time.  Residents and property owners along Lake St. Louis near Montreal and the lower St. Lawrence River should be aware that water levels will continue to be kept very high and that low lying areas may see minor impacts.

These deviation strategies are being implemented in a very specific window of opportunity and will help remove an additional amount of water from Lake Ontario in the coming weeks before the Ottawa river freshet begins; at which time the Lake Ontario outflows will need to be reduced significantly until the Ottawa river flows from melted snow has receded.

Please note that the Board has recently created a new website page focused on the recent high-water events: All high-water related materials are now in one 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 Please consult your local officials for flood preparedness and response measures.


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.