Moses Saunders Dam

Record Outflows to Continue Through the Summer


Water levels are declining throughout the system as warmer, drier weather and record Lake Ontario outflows of 10,400 m3/s (367,270 cubic feet per second) continue. 

At its meeting on July 5th, the Board reached consensus to maintain the current outflow, which is 200 m3/s (7,060 cfs) higher than regulation Plan 2014 and the maximum safe navigation limit that would normally apply at these lake levels. The Seaway Corporations have implemented mitigation measures to allow safe navigation to continue at these higher flows, which will continue to lower Lake Ontario levels and provide relief to those impacted by this year’s high water event.

The Board deliberated several outflow strategies above 10,400 m3/s and considered both the additional decline on Lake Ontario and impacts to other stakeholders. These scenarios included incremental increases all the way up to maximum outflow capacity of the St. Lawrence River. At present, any additional increase in flow would require the Seaway Corporations to shut down shipping on the St. Lawrence River between St. Lambert and Cape Vincent. The economic costs for disrupting the supply chain of the Great Lakes-St. Lawrence economy is estimated at $50,000,000 per day. Additional impacts were also expected for recreational boating and downstream shoreline property owners, including resumed and additional flooding in areas of the lower St. Lawrence River just upstream of Montreal. Additional environmental impacts were also expected due to sustained high flows, including impacts to fish, wildlife and waterfowl habitat and breeding grounds.

Outflows at maximum system capacity for 4 weeks would hasten the recovery of Lake Ontario in the short-term; however, when compared to maintaining the current record high outflow strategy both options converge to within 1 inch by December 31st. This is because the amount of water that can be physically passed down the St. Lawrence River is directly related to the level of Lake Ontario. As the lake declines, so does maximum river capacity. Maintaining the current major deviation strategy will provide comparable benefit by the end of the calendar year, without creating $1.4 billion in economic damages. 

The Board has also agreed to maintain the flow at 10,400 m3/s (367,270 cfs) for a longer duration than in 2017, until water levels on Lake Ontario drop more than 30 cm (1 foot) and fall below 75.50 m (247.7 ft).  Current forecasts suggest this may occur around mid-August, depending on water supplies. 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 into the fall to continue lowering Lake Ontario levels at an accelerated rate. The Seaway Corporations will maintain mitigation measures to ensure safe navigation can continue during this period.

These enhanced outflow measures will help to provide both immediate and longer-term relief to all impacted upstream shoreline residents and property owners due to the high water levels. The intent of the Board is to lower water levels as much as possible prior to winter. It should be noted that the Board can only control outflows and not the water supplies to Lake Ontario. While the higher outflows will accelerate the rate of lowering that would otherwise occur, it is not possible, this year or any other, to lower Lake Ontario to a predetermined “safe” water level by the onset of winter.

The International Joint Commission has asked the Great Lakes-St. Lawrence River Adaptive Management (GLAM) Committee to expedite their ongoing review of Plan 2014. The Board will release a statement later this week describing the extents of the GLAM assessment.

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.