International Lake Ontario - St. Lawrence River Board

Outflows Maximized to Further Reduce Lake Ontario


Record-breaking natural conditions have exceeded the capability of water level regulation to prevent the wide-spread flooding and coastal impacts experienced across the Lake Ontario – St. Lawrence River basin. Gradually decreasing inflows from Lake Erie, drier weather and record-setting outflows on the St. Lawrence River have resulted in a steadily declining Lake Ontario, down 45 cm (17.7 in.) below the peak. The Board will continue to prescribe the most aggressive outflows with the goal of reducing Lake Ontario as quickly and safely as possible.

The Board met on 15 August 2017 to assess current conditions and hydrologic forecasts, and review the ongoing impacts of high water levels and flows throughout the Lake Ontario – St. Lawrence River system. Outflows will continue at 9910 m³/s (350,000 cfs) until midnight tonight, when they will be lowered slightly to 9870 m3/s (348,600 cfs), which will remain the highest flow ever recorded at this time of year. High outflows remain necessary to provide relief to those affected by this year’s high water levels on Lake Ontario, but the decrease is necessary to balance the impacts to navigation and other interests in the St. Lawrence River.

Ottawa River flows into the St. Lawrence River have decreased and, while levels of Lake St. Louis (near Montreal) continue near record highs for this time of year, they are now below flood levels. However, the unprecedented outflow from the Moses-Saunders Dam has resulted in the lowest water levels experienced on Lake St. Lawrence (near Cornwall, Ontario and Massena, NY) since 1998. Falling water levels will result in increased currents and potentially hazardous navigation conditions for all in the international section of the St. Lawrence River.

Thus, the Board will continue to maximize outflows in consideration of impacts to public water uses, riparian landowners and businesses, commercial shipping and recreational boating. Water levels are expected to continue to decline rapidly into the fall throughout the system. The Board, in conjunction with its staff, continues to monitor and reassess conditions on an ongoing basis.

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

Gail Faveri: (905) 336-6007;
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 stlaw-L-subscribe@cciw.cawith the word ’subscribe’ in the title and body of your message.