Moses Saunders Dam

Lake Ontario outflows continue to be adjusted to balance high water levels


With Lake Ontario caught between a flooding Lake Erie and a flooded lower St. Lawrence River, outflows from Lake Ontario continue to be frequently adjusted to balance the impacts of high water levels that are occurring throughout the Lake Ontario – St. Lawrence River system.

Several months of wet weather followed by especially heavy rains and snowmelt over the past few weeks caused record-breaking Ottawa River flows and resulted in severe flooding along both the Ottawa and lower St. Lawrence River.  Outflows from Lake Ontario were temporarily reduced, helping to mitigate – but not eliminate – the impacts in the lower St. Lawrence during the peak of this event.  Lake Erie water levels have been above seasonal records since the end of April and exceeded historic record highs at the start of May. Record inflows from Lake Erie combined with the reduced outflows to cause Lake Ontario levels to rise rapidly over the past several weeks.

Lake Ontario water levels remain below the record highs of 2017 currently, but have reached the criterion H14 high level that applies this time of year, authorizing the International Lake Ontario – St. Lawrence River Board to deviate from regulation Plan 2014.

At this time, with high water impacts continuing both upstream and downstream, the Board has reached consensus to continue to adjust outflows according to the F-limit rules of Plan 2014. The F-limit balances high levels upstream on Lake Ontario and the upper St. Lawrence, with those downstream on Lake St. Louis and the lower St. Lawrence.  St. Lawrence River levels at Lake St. Louis near Montreal will be maintained at 22.48 m as Lake Ontario has now risen to 75.60 m.  Lake Ontario outflows had been increasing rapidly in recent days, but heavy rains have caused Ottawa River flows to rise again, and temporary outflow reductions are expected to be required over the next few days.  Lake Ontario outflows will be increased again as soon as conditions allow and as rapidly as possible.

Uncontrolled inflows from Lake Erie through the Niagara River and precipitation continue to be the main driver of water levels.  The Board is constantly monitoring the situation and making use of every opportunity to adjust outflows, with the intent to balance high water levels in the interests of all stakeholders, and to regulate Lake Ontario outflows to provide all possible relief to shoreline property owners and communities both upstream and downstream of the Moses-Saunders Power Dam.

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 75.88 m (248.9 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.