Moses Saunders Dam

Lake Ontario outflows to be increased above navigation limit


The International Lake Ontario – St. Lawrence River Board (Board) will continue to increase outflows to provide relief to shoreline interests on Lake Ontario after it agreed to raise flows above the regulation plan’s maximum L-Limit, considered to be the safe threshold for commercial navigation.

Outflows reached 10,200 m3/s (360,200 cfs) yesterday and the Board will commence incrementally raising outflows by 50 m3/s (1,760 cfs) per day on Monday, June 10th. Outflows will be increased by 50 m3/s (1,760 cfs) increments until 10,400 m3/s (367,270 cfs) is reached on 13 June, 2019.  10,400 m3/s is the maximum flow that was attained in 2017 and the maximum sustained flow on record.  The St. Lawrence Seaway has been advised of this strategy.  The Board will also continue to explore further increases based on conditions within the system at that time.

The purpose of increasing outflows incrementally is threefold: 1. Lake St. Louis remains above the final F-limit tier and is still in flood; 2. to provide time to put further mitigation measures in place; 3. and to keep Lake St. Lawrence levels from undue drop while OPG repairs a crane at Iroquois Dam.   

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 75.88 m (248.9 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.