Moses Saunders Dam

Lake Ontario reaching peak, outflows increased rapidly


Lake Ontario water levels have started to stabilize due to decreased precipitation and increased Lake Ontario outflows, which have been increasing rapidly as Ottawa River flows have continued to drop from their record highs this spring.  

Outflows reached 10,000 m3/s (353,100 cfs) yesterday, close to the highest on record, and further increases are expected. 

Extraordinarily high outflows combined with forecasts of warmer, drier conditions later this week, make it likely that Lake Ontario is at or very near its peak level this year.  Any additional rise is likely to be small, less than 3 cm (1 in.) depending on rainfall, and there is a good chance levels will remain stable or even start to decline slowly next week.

With levels above average their remains the possibility for locally higher levels, especially during periods of active weather, and the Board reminds everyone to refer to local forecasts for conditions and warnings specific to your area. 

The Board continues to monitor the situation, makes use of every opportunity to increase outflows, and consider all possible measures to provide relief from the record-high water levels.  

Extreme high levels are never normal, but they have occurred in the past and they will occur again in the future.  The primary causes of high water levels are always the same - wet weather.  Record precipitation caused the record high water levels in 2017, and it led to record inflows from Lake Erie and the Ottawa River system, resulting in new record highs this year.  Such conditions are uncontrolled and highly unpredictable, and this has always been the case.  The new normal is that we must make the preparations for the next event a part of everyday practice and planning, even though it is becoming especially difficult to know how soon that next event will be.   

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, (716) 352-8669;


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 75.88 m (248.9 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.