International Lake Ontario - St. Lawrence River Board

Board to Increase Outflows June 14 - Lake Ontario Begins Slow Decline


At its conference call on Monday, the International Lake Ontario – St. Lawrence River Board decided to temporarily increase the outflow from Lake Ontario from 10,200 m3/s (360,200 ft3/s) to 10,400 m3/s (367,300 ft3/s) for 72 hours with the hope of sustaining the increase for a longer period of time after a short testing phase.  Since maintaining a continuous outflow of 10,400 m3/s is historically unprecedented, the Board along with the operators of the Moses-Saunders dam and navigation agencies will assess the safety of conditions before committing to sustaining this outflow for a longer duration. In particular, because the increased outflows will raise current velocities in the St. Lawrence River, the St. Lawrence Seaway has deployed significant additional mitigation measures to maintain safe conditions and ensure commercial navigation can continue during this period of exceptionally high flows.

With downstream water levels on the decline and Lake Ontario still above previous maximum levels for this time of year, the Board continues to explore options to provide all possible relief to riparian owners on Lake Ontario while considering impacts to all stakeholders within the system.  The level of Lake Ontario has gradually declined 7 cm (2.8 in.) since the peak level of 75.88 m (248.95 ft) last recorded on 29 May.  Water levels downstream on the St. Lawrence River at Lake St. Louis near Montreal have declined 23 cm (9.1 in.) since 29 May.  With the weather conditions forecasted over the coming days, water levels upstream and downstream are expected to continue to fall. 

On 13 June 2017, Lake Ontario was 75.81 m (248.72 ft), 76 cm (29.9 inches) above its long-term average level for this time of year. The level at Lake St. Lawrence was 16 cm (6.3 inches) above average, while the level at Lake St. Louis was 22.23 m (72.93 ft), 87 cm (34.2 inches) above average. At Montreal Harbor, the level was 109 cm (42.9 inches) above average.  

The Board continues to monitor the system and will convene again on 19 June 2017 to assess the impacts from the change in outflow. Information can be found on the Board’s Facebook page at, and more detailed information is available on its website at


Gail R. 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 75.88 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 ( 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, with the word ’subscribe’ in the title and body of your message.