Moses Saunders Dam

Lake St. Lawrence water levels to decline following long September weekend


With summer nearing an end, the Board will adjust its outflow strategy and allow Lake St. Lawrence levels to decline to the normal navigation season minimum following the September long weekend. This decision will allow for slightly more water to be released from Lake Ontario during the fall.

The lower and declining levels on Lake Ontario combined with the high outflows through the Moses-Saunders Power Dam are resulting in very low levels on Lake St. Lawrence that are anticipated to continue. This was the fourth straight summer of well-below-average levels of Lake St. Lawrence, which as the forebay to the dam, responds much more rapidly and significantly to increases in outflows than the much larger Lake Ontario upstream.

During the 22 May teleconference, the Board agreed to tap into the accumulated water removed from Lake Ontario, if needed, to maintain levels on Lake St. Lawrence above 73.0 m or 239.50 ft (40 cm or 16 inches above the usual navigation-season low limit) until after the 7 September long weekend. The Lake Ontario outflow was decreased slightly last week (at noon on 17 August) to allow Lake St. Lawrence levels to increase back up to approximately 73.0 m (239.50 ft) following a period of sustained easterly winds that resulted in lower levels there.

As fall weather approaches, recreational boating activity begins to decrease. With high inflows from the upper Great Lakes continuing and Lake Ontario levels remaining 13 cm or 5 inches above their long-term average value for this time of year, the Board has decided to cease the maintenance of levels on Lake St. Lawrence above 73.0 m following the 7 September long weekend. Levels of Lake St. Lawrence can be expected to decline following 7 September, so residents and other recreational boaters are encouraged to remove all of their associated equipment from the waterfront on or prior to the September long weekend.

Lake Ontario levels peaked early this year at 75.40 m (247.38 ft.) on 5 May, 10 cm (4 inches) below the general flood stage and over a half meter (20 inches) lower than the peak in 2019. Lake levels are expected to continue their seasonal decline through summer, and have fallen 41 cm or 16 inches from the crest to date.

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.