International Lake Ontario - St. Lawrence River Board

Outflows from Lake Ontario Break February Record, Water Levels Gradually Improving


The average Lake Ontario outflow during the month of February was the highest in recorded history.  Historical records start in 1900 and include outflows that occurred both prior to and since the beginning of regulation in 1960.  A stable ice cover in the St. Lawrence River allowed Plan 2014 to increase outflow under the ice, and as a result, Lake Ontario levels have fallen below those recorded at this time in 2017.

Plan 2014 continues to prescribe near-record outflows in response to above-average levels of both Lake Ontario and the upper Great Lakes.  Following temporary flow reductions during the extreme cold weather at the start of the year that saw ice form quickly on the St. Lawrence River, outflows were quickly increased thereafter, to the maximum possible without causing flooding on Lake St. Louis near Montreal.

Basin conditions allowed Plan 2014 to prescribe record high outflows in February, even while Lake Ontario remained below  Criterion H14 ”trigger” levels. In instances when Lake Ontario reaches its high water trigger level, criterion H14 gives the board the authority to deviate from Plan 2014 in order to provide all possible relief to riparian property and businesses upstream and downstream. However, the use of this authority must still consider the effects of outflows on all interests, including the risk of flooding on Lake Ontario, the risk of flooding downstream and the risk of ice jams in the St. Lawrence River.

Currently the water level of Lake Ontario is 74.96 m (245.93 ft), which is 30 cm (11.8 in) above average, and 3 cm (1.2 in) below last year.  The level of Lake St. Louis near Montreal is now 54 cm (21.3 in) above average and 26 cm (10.2 in) above its level of a year ago.  Water levels on the upper Great Lakes, Lake Ontario and the St. Lawrence River are forecast to remain above average moving into the spring.  As a result, Plan 2014 will continue to release high outflows taking into consideration all interests throughout the Lake Ontario – St. Lawrence River system.     

The Board notes that, while Lake Ontario remains well above average, historically, water levels in winter have not provided an accurate indicator of the peak later in spring.  Weather and hydrologic conditions play a much greater role than water regulation in influencing water levels, and while impossible to predict, the probability of a repeat of last spring’s exceptional rains and subsequent high water levels is low.  Nonetheless, extreme conditions may occur in any given year, so shoreline property and business owners, and local government officials should always be prepared for a full range of water levels on Lake Ontario at any given time in the future.

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, including graphics and photos, are available on the Board’s website and posted to the Board’s Facebook page at (English).


Rob Caldwell: (613) 938-5864;

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 (248.95 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.