Moses-Saunders Dam

High Lake Ontario Outflows Continue, Impacts Felt Across the System


Following the closure of the Seaway, and some partial and temporary ice formation in early January, mild temperatures across the Lake Ontario basin have allowed the International Lake Ontario - St. Lawrence River Board to set Lake Ontario outflows at unprecedented levels, higher than has ever previously been released in winter for several days and at times up to 10,700 cubic meters per second or 377,900 cubic feet per second.

These very high outflows are only possible under the current conditions and may only continue during a relatively short window before temperatures fall and ice formation resumes.  At that time, outflows may need to be reduced to avoid disrupting the ice cover as it forms and stabilizes.  This may happen as early as Wednesday, January 8th.  However, if mild weather follows and ice conditions allow, outflows will be increased again as much and as soon as possible.

Even with unprecedented outflows from Lake Ontario the relative impact on the lake level will be small, during a time of year when water levels typically rise, with the key drivers for the lake levels being extremely high inflows from Lake Erie and any precipitation that continues to fall across the basin. 

The Board will continue to set outflows as high as possible based on changing conditions throughout the basin. In addition to ice formation in the St. Lawrence River, other critical conditions that have been identified over the past week of high outflows are maintaining a minimum water level difference upstream and downstream of Moses-Saunders Dam for safe operation and flow monitoring of the power generation plant, high water levels downstream of the dam specifically around Lake St. Louis, lower water levels on Lake St. Lawrence upstream of Moses-Saunders, and wind-driven water level changes.

Over the next several weeks, as stated in a previous release, regulated outflows will remain as high as feasible based on river conditions. As a result, residents around Lake St. Lawrence are warned to expect both extreme high and low water levels this winter, as the Board implements its winter deviation strategy. Extreme low water conditions are occurring now under the very high outflows being released.  High water conditions will occur on Lake St. Lawrence whenever outflows are reduced to allow for stable ice cover formation.  The winter deviation strategy aims to take full advantage of all opportunities to safely maintain maximum possible outflows and help reduce the probability of high water conditions occurring this year on Lake Ontario. 

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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.