International Lake Ontario - St. Lawrence River Board

Board Continues to Maximize Outflows as Wet Weather Persists


Following record setting wet weather in April and May, heavy rains and storms have been frequent and widespread June through mid-July, resulting in continued wet conditions and causing high water levels to persist throughout much of the Lake Ontario - St. Lawrence River system.  The Board continues to release the unprecedented outflow of 10,400 m3/s (367,300 cfs) with the intent of providing all possible relief to Lake Ontario shoreline property owners, boaters, and other affected interests, while balancing the impacts on other affected stakeholders in the system.  

The Board continues to meet regularly to assess current and forecast hydrologic conditions.  Over the past several weeks, inflows to Lake Ontario from Lake Erie and the Lake Ontario basin itself have remained above average.  Relatively high Ottawa River flows have also continued.  Nonetheless, since peaking in late May, water levels have been generally declining on Lake Ontario, and it is now 20 cm (7.9 inches) below the peak level last recorded May 29th.  St. Lawrence River levels have also been falling, including at Lake St. Lawrence, immediately upstream of Moses-Saunders Dam, and at Lake St. Louis near Montreal, where levels were 47 cm (18.5 inches) below the highest levels recorded earlier this spring.  

In light of these conditions, the Board also discussed current and expected outflows from Lake Ontario.  When setting the outflow, the Board must consider the effects on the entire Lake Ontario – St. Lawrence River system.  The Board understands that severe hardships continue to be incurred by Lake Ontario residents and business owners alike due to continuing high lake levels, associated flooding and related damages.  The Board has set the current high outflow in an attempt to best alleviate these impacts, but recognizes that any further increases in outflow would only provide a few centimeters (or about an inch) of additional relief to Lake Ontario per week, while causing rapid and significant changes to St. Lawrence River conditions and substantial adverse socio-economic and ecological impacts throughout the region.  

Notably, recent high outflows have already increased currents and reduced depths in the upper St. Lawrence River, between Moses-Saunders Dam and the Thousand Islands area.  The Board concludes that any further increase in outflow would jeopardize the safety of ships or halt commercial navigation.  This would also cause many coastal lands along the St. Lawrence to be subject to potential shoreline erosion.  Such increases would also substantially reduce water levels at Lake St. Lawrence, impacting near-shore habitat and recreational boating in this stretch of the river, and potentially municipal water intakes under the highest flow scenarios.  Additionally, increases in outflow may induce further flooding on the lower St. Lawrence River, where like on Lake Ontario, hundreds of residents have already been impacted over the past several weeks, including at Lake St. Louis in the Montreal area, all the way to Lake St. Peter and the city of Trois-Rivières in the province of Quebec.    

The Board, in consideration of all of these factors, has decided to remain at the current record outflow in order to maximize the rate of decline in Lake Ontario levels, while limiting the impacts on other interests throughout the system. Water levels are expected to continue to decline into the fall and winter throughout the system.  As they do, the Board, in conjunction with its staff, will continue to monitor and reassess conditions on an ongoing basis. 

Information on hydrologic conditions, water levels and outflows, including graphics and photos, are posted to the Board’s Facebook page at (English), and additional information is available on its website at   


Derrick Beach: (905) 336-4714;

Arun Heer: (513) 684-6202; 

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 75.73 m (248.5 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 ( To 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.