Moses-Saunders Dam

Lake Ontario outflow sets records in 2019, further increases expected in New Year


Outflows will be increased substantially in the coming days as efforts to remove water from Lake Ontario continue.

Starting tomorrow, following the end of navigation season, outflows will be increased as much as possible until ice formation resumes on the St. Lawrence River. A flow increase from 8,850 m3/s (312,500 cfs) to over 10,000 m3/s (353,000 cfs) may be possible in the coming days, with the exact amount depending on ice and water level conditions in the St. Lawrence River.  Water levels downstream of the Moses-Saunders Dam, including around the Montreal area, are expected to rise, but will be monitored closely to ensure they are maintained below flood levels.

Lake Ontario outflows were first set to record-rates in June as water levels of Lake Ontario reached a new daily record-high of 75.92 m (249.08 ft).  This followed an unprecedented spring that saw record water levels and flows occurring across the Great Lakes and Ottawa River basins.  High outflows from Lake Ontario continued through the summer, fall and early winter, resulting in more water released from Lake Ontario during the last seven months of 2019 than in any year since the start of records in 1900.  The average outflow from June through December was 9,560 m3/s (337,600 cfs), the highest flow ever released over this period, and equivalent to removing nearly 9.1 m (30 ft) of water from Lake Ontario during this time. 

However, with all of the Great Lakes seeing record or near-record water levels in 2019, inflows to Lake Ontario have also remained high during that time.  Lake Ontario’s level was 75.00 m (246.06 ft) yesterday and remains well-above seasonal averages.  High inflows are expected to continue into 2020. 

The International Lake Ontario – St. Lawrence River Board, under authority granted to it by the International Joint Commission, will continue to deviate from Plan 2014 and will look for any and all opportunities to remove additional water from Lake Ontario prior to the spring. 

The first of these opportunities is expected at the start of January.  Over the past several weeks, outflows were set at 200 m3/s (7,100 cfs) above the Plan 2014 maximum L-limit, which is the highest outflow that can be released from Lake Ontario, while still ensuring safe navigation through the St. Lawrence River.  However, with the St. Lawrence Seaway season set to end on December 31st, this constraint will no longer apply. 

Ice conditions are also no longer a constraint.  Flows were temporarily reduced on December 20th following a brief cold spell that resulted in temporary ice formation in the Beauharnois Canal.  Mild temperatures followed, causing the ice cover to deteriorate and allowing outflows to again be rapidly increased.  Ice formation will likely resume during the next cold spell, but the timing is uncertain.

The Board, in conjunction with its staff, continues to monitor conditions on an ongoing basis. 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.