Maintaining Record Outflows as Lake Levels Decline


Lake Ontario water levels continue to decline slowly as the Board is maintaining record outflows of 10,400 m3/s (367,270 cubic feet per second). 

At its meeting on July 19th, the Board deliberated several outflow strategies above 10,400 m3/s and considered both the additional decline on Lake Ontario and impacts to stakeholders. These scenarios included incremental increases all the way up to maximum outflow capacity of the St. Lawrence River.

The Board has agreed to maintain the flow at 10,400 m3/s (367,270 cfs) until water levels on Lake Ontario drop approximately 30 cm (1 foot) and fall below 75.50 m (247.7 ft).  Current forecasts suggest this may occur around mid-August, but again, this is depending on water supplies (i.e. Lake Erie inflow and Lake Ontario basin weather patterns). In addition, the Board has notified the Seaway Corporations that it will continue to set outflows at approximately 200 m3/s (7,060 cubic feet per second) above the normal safe navigation flow limit as defined by the regulation plan into the fall to continue lowering Lake Ontario levels at an accelerated rate. Maintaining the current major deviation strategy will provide greater reductions in water levels than prescribed Plan flows by the end of the calendar year.

The intent of the Board is to lower water levels as much as possible prior to winter. The Board is currently investigating the historic data on regulation impacts during previous high water events.  This data will help inform the Board on what the impacts of its’ regulatory decisions are on all interests during extraordinary high water events.  It is important to remember that the Board can only control outflows and not the water supplies to Lake Ontario. High water supplies means that water level reductions will take longer than under lower water supplies.  The Board is acutely aware and concerned for the welfare of the many shoreline property owners who continue to see impacts from the high water level and continues to consider all regulation strategies that would provide the most possible relief to those impacted.  However, the limitations of the Lake Ontario St. Lawrence River system prevent another regulation strategy that would provide more immediate possible relief without significantly impacting other interests.

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.