International Lake Ontario - St. Lawrence River Board

Board Continues to Maximize Outflows from Lake Ontario


At its meeting on June 30th, the International Lake Ontario – St. Lawrence River Board agreed to continue releasing an outflow of 10,400 cubic metres per second (m3/s) (367,300 cubic feet per second), as conditions allow, in order to help lower the level of Lake Ontario, and provide all possible relief to riparian residents while considering the impacts throughout the Lake Ontario – St. Lawrence River system. This outflow continues to be the highest ever released from Lake Ontario on a sustained basis.

The Board reviewed current conditions of Lake Ontario and the St. Lawrence River, and despite efforts to provide relief by releasing record-high outflows, recent wet conditions continue to sustain high water levels, causing continued severe impacts to Lake Ontario and St. Lawrence River property owners, recreational boaters, businesses and tourism. Lake Erie remains well above average, and combined with significant rainfall during the past month, the total inflow to Lake Ontario was the 2nd highest recorded in the month of June since 1900. Yet despite the near record-high inflows and notwithstanding a slight rise in levels following especially heavy showers and thunderstorms on June 22nd, Lake Ontario levels fell 9 cm (3.5 inches) overall last month, 8 cm (3.1 inches) more than average and the 11th largest decline in June since 1918. On the St. Lawrence River, levels near Montreal and further downstream had been declining in general, but rose to near record highs in recent days following a series of storm events. The Board continues to monitor and assess conditions in consideration of the impacts that these exceptionally high levels and flows are having in Lake Ontario and the upper and lower St. Lawrence River on all stakeholders, including commercial navigation.

Furthermore, based on information provided to the Board by the St. Lawrence Seaway on navigation conditions at high flows, the Board concluded that an outflow of 10,400 m3/s (367,300 cfs) is the maximum outflow that can be released from Lake Ontario with present river levels, that would still allow continued, though restricted, safe commercial navigation in the St. Lawrence River. The Board noted that while wet weather has maintained high levels recently, warmer and drier summer conditions are likely to return, and allow water levels throughout the system to resume their decline.As levels decline, a gradual reduction in outflows will be required to prevent the velocities in the St. Lawrence River from exceeding the limits for safe navigation. However, the Board expects the flow of 10,400 m3/s (367,300 cfs) can safely be maintained for some time to come, and will continue to re-evaluate this on a daily basis at least until its next meeting.

The Board is drawing on all of its resources and available technological support to provide the best information and allow it to review options to reduce water levels as fast as possible while considering all interests in the Lake Ontario – St. Lawrence River system. The Board appreciates the input of all stakeholders and interests and looks forward to continuing open communication during this period of historic high water levels.

Outflow changes, photos, and graphs are posted to the Board’s Facebook page at (English), and more detailed information is available on its website at

Derrick Beach: (905) 336-4714;
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.