Moses-Saunders Dam

Water Levels in the Lake Ontario St. Lawrence Will Continue to Rise


A major flood event is under way in the lower St. Lawrence River with levels in some areas above 2017 peaks, while levels throughout the Lake Ontario - St. Lawrence River system are expected to keep rising significantly this coming week due to rainfall across the basin. 

The Lake Ontario outflows are being adjusted as Ottawa River flows into the St. Lawrence River near Montreal continue to increase, in order to balance high levels upstream on Lake Ontario and the upper St. Lawrence, with those downstream on Lake St. Louis and the lower St. Lawrence.

Lake Ontario outflows will continue to be adjusted on a frequent basis to balance Lake Ontario levels with those downstream in response to dynamic conditions, but it is still expected that water levels on Lake Ontario will rise more than is typical this time of year.  How much they will rise will depend on weather conditions in both the Ottawa River and Lake Ontario basins.  Another factor contributing to Lake Ontario water levels is the inflow from Lake Erie that continues to be extremely high due to above average water levels on Lake Erie.   

A significant storm with heavy rainfall is expected to spread across the basin today. Widespread areas are expected to see 25 to 50 mm (1 to 2 in.) of precipitation and rapidly increasing surface runoff in the Lake Ontario, St. Lawrence and Ottawa River basins.

With heavy and widespread rain forecasted, the Ottawa River is predicted to reach unprecedented outflows, resulting in higher levels in the lower St Lawrence River and temporary reductions in Lake Ontario outflows.

With the heavy rainfall expected within the Lake Ontario basin itself, and likely reduced outflows due to downstream flooding, a significant rise in lake levels is expected. It is worth noting that measured and forecast water level conditions can be subject to a high degree of uncertainty and do not account for local variations due to wind and wave effects.

Until the rain falls, we will not know the extent of the impacts.  Public information is available online through the ILOSLRB website: and on Facebook:

*** Emergency response is typically provided through your local municipality ***

Current Conditions can be found here:  

Forecasts can be found here:

For further information on conditions locally, please refer to the responsible authorities in your area, a short list is provided below.






New York State



Canadian: Rob Caldwell: (613) 938-5864;

United States: 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 75.88 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.