Moses-Saunders Dam

Outflow Remains at Seasonal Record High, Lake Ontario continues to decline


To provide the highest attainable relief to all interests, both upstream and downstream of the Moses-Saunders Dam, outflows remain at record-high rates for this time of year, eclipsing the outflows released at this same time in any other years dating back to 1900.  As Lake Ontario continues its seasonal decline, the outflows now and for the foreseeable future will remain at the maximum rate possible given shoreline property owner’s interests and safety considerations throughout the Lake Ontario - St. Lawrence System.

The Board considers outflow limitations defined and prescribed in the approved regulation Plan 2014 when setting the outflows during extreme conditions. During extreme conditions the Board is designated with the authority to deviate from plan flow to provide relief to one or more interest groups. In doing so, the Board is required to weigh the impact of providing relief against the benefit. Outflows of this magnitude are subject to multiple constraints of the Lake Ontario - St. Lawrence system. The Board reached consensus that the current outflow is the highest currently possible, which provides the most relief to shoreline property owners upstream and downstream and provides safe conditions for all other interests.  Information on the outflows can be found on the Board’s website

Significant impacts of the 2019 high water event throughout the Lake Ontario-St. Lawrence River system are due to record-high water supplies into Lake Ontario over the 8-month period from November through June, and the record volume and peak flows in the Ottawa River from April through May. 

The unprecedented conditions and record water levels that followed caused damage to many residents and communities over the summer and some of these impacts continue today, even with flood conditions diminished in the system. It will take time - even with well above average outflows - for the water levels to go down as inflows from Lake Erie continue to be well above average.  Water levels are primarily driven by water supplies, not by the outflows.  The outflows are also constrained by physical limits of the river system.

Continuous outflows of 10,400 m3/s were possible this summer with a series of additional safety measures required by the St. Lawrence Seaway administration. This flow was based on the record high Lake Ontario elevation; however, as the lake levels decline flows must be reduced to maintain the same balanced level of impact. River velocities increase as the same volume of water passes through a lower and narrower river.  Lake Ontario has been declining relatively rapidly in recent weeks, making it necessary to reduce outflows and manage dangerous river currents.

Given the current conditions, velocities are higher than normal throughout the river and they are causing potentially unsafe cross-currents with erosion impacting many interests in the St. Lawrence River. Sustaining or increasing velocities would cause conditions to become much worse.  Even with the weekly reductions, the outflows will remain at the highest rates ever for the time of year to provide all possible relief to shoreline property owners both upstream and downstream.

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.