Moses-Saunders Dam

With Lake Ontario water levels declining, Board adjusts outflow strategy


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 6 cm (2 in.) from the crest to date.

Lower Lake Ontario levels and the continuing high outflows are causing increased currents in the upper St. Lawrence River and also extremely low levels on Lake St. Lawrence, the forebay just upstream of the Moses-Saunders Power Dam. The International Lake Ontario – St. Lawrence River Board has assessed the situation carefully and, if necessary, will act to augment low levels at this location over the coming weeks.

The Board’s extended general deviation authority (as granted by the International Joint Commission (IJC) on 9 October 2019) has ended. The Board is no longer deviating by releasing outflows above Plan 2014 prescribed flows, since Lake Ontario reached its peak and began its seasonal decline. The peak level of Lake Ontario is still well above average, but was reduced by 18 cm (7 in.) owing to deviations from Plan 2014. These deviation totals accumulated over the past several months as the Board attempted to remove as much water as possible from Lake Ontario, prior to spring. 

Drier conditions have prevailed in recent weeks, including around Lake Ontario and in the Ottawa and lower St. Lawrence River basins. These are the primary reasons for the recent decline in Lake Ontario levels, which has occurred despite very high inflows from the extremely high upper Great Lakes. These high inflows will continue for the foreseeable future and, in response, Plan 2014 will continue to prescribe very high outflows, which will enhance Lake Ontario’s seasonal decline.

However, the lower and declining levels on Lake Ontario combined with the high outflows through the Moses-Saunders Power Dam that will continue are resulting in very low levels on Lake St. Lawrence that are anticipated to persist for months to come. This will be the fourth straight summer of well-below-average levels of Lake St. Lawrence, which responds much more rapidly and significantly to increases in outflows than the much larger Lake Ontario upstream. Had the Board not deviated and removed water from Lake Ontario since last spring, Lake St. Lawrence would currently be approximately 14 cm (6 in.) higher.

On a 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. As the Board returns to plan flows, Lake St. Lawrence is expected to remain above this threshold for several weeks unless winds cause it to temporarily fall below.

Note that maintaining Lake St. Lawrence levels above 73.0 m (239.5 ft) under actual conditions wetter than normal will require no flow reductions which might cause higher Lake Ontario levels. Wet conditions would cause higher Lake Ontario levels, which would result in Lake St. Lawrence levels above 73.0 m, even with high outflows. Maintaining Lake St. Lawrence levels would also have no impact on levels heading into 2021 under such wet conditions and the Board emphasizes that lake level and other conditions at the end of 2020 are poor indicators of what levels will be like in 2021. The primary factors are what Lake Erie inflows and Lake Ontario – St. Lawrence River basin snowmelt, runoff and precipitation conditions are experienced next spring.  

Augmenting Lake St. Lawrence levels may occur if very dry conditions result in lower Lake Ontario levels. At most, this would result in Lake Ontario levels up to 8 cm (3.2 in.) higher by 7 September than what they would be without this strategy, but only under the very driest water supply scenarios where Lake Ontario is much lower on its own. Most scenarios result in much smaller differences. Differences will be further reduced through the fall, such that, by the end of 2020, there is expected to be almost no difference in levels throughout the Lake Ontario – St. Lawrence River System. 

Shoreline businesses and property owners are reminded that the GLAM Committee continues to host an online questionnaire to allow for direct reporting on impacts related to recent high water conditions that can be incorporated into the expedited review effort. The 2020 version of the questionnaire is now available on the GLAM Committee's website:

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.