Moses-Saunders Dam

Lake Ontario outflows to be maintained at record highs


The Board is doing everything possible to provide all possible relief to Lake Ontario and upper St. Lawrence River residents, while considering impacts throughout the system. During its meeting on 21 June, the Board decided to maintain outflows at their current record-high  levels, 10,400 m3/s (367,270 cfs), for the next week considering there is very little  capacity for passing water on the lower St. Lawrence River due to Lake St. Louis flooding conditions.  Many areas around Montreal and Lake St. Louis still remain flooded presently.

Significant precipitation over the last few days throughout the system have increased outflow from the Ottawa River into the lower St. Lawrence River.  This has caused water levels on Lake St. Louis to rise to 22.42 m (73.56 ft) again, only 6 cm (2.4 in) below the levels causing significant flooding. 

Before making their decision to maintain the current outflow, the Board considered the impact of increased currents and flows on multiple stakeholders, and received testimony from various groups, such as shoreline owners, hydropower, municipal and industrial water uses, recreational and commercial navigation, ecosystems, and upstream and downstream conditions.

Even with high outflows, it is expected that Lake Ontario will remain stable or decline slowly for the next several weeks. The Board continues to seek any opportunity to lower Lake Ontario faster than what is presently possible, and will be meeting again this week to review its regulation strategy.

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 75.92 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.