Drone shot of Moses-Saunders Dam

Lake Ontario and the upper St. Lawrence River Flood Risk Diminishes; Very High Outflows to Continue


The risk of flooding on Lake Ontario and the upper St. Lawrence River has declined from moderate in December 2020 to low. In December, the risk analysis indicated a 28% chance of water levels exceeding a threshold at which damages occur in many shoreline communities. The risk is now down to 8%. There is a comparable risk of flooding on Lake St. Louis in the lower St. Lawrence River.

This risk reduction is largely the result of dry conditions throughout the Great Lakes Basin in January and February. Lake Ontario water levels declined 8 cm in January and 7 cm in February. Lake Ontario’s level is currently 11 cm (4.3 in) below the long-term average (LTA) level for this time of year. The lake level is almost 2 ft (58 cm) lower than at this time a year ago and the lowest it has been at this time of year since 2015.

The Board continues to closely monitor the persistently high levels and flows from Lake Erie, which flows directly into Lake Ontario.  In response, Plan 2014 continues to call for very high outflows from Lake Ontario.  However, it is also noted that the Lake Erie level has also declined and is now more than a foot lower (more than 30 cm lower) than it was at this time last year, which means inflows from Lake Erie have begun to moderate.  Given these factors, the Board has decided to cease deviating from Plan 2014 effective on 1 March and revert to the high outflows prescribed by Plan 2014.  The Board received authority from the International Joint Commission (IJC) to deviate from Plan prescribed flows from 1 January through the seasonal crest of Lake Ontario this year.  Under this authority, the Board deviated above Plan prescribed flows from January through February as ice conditions allowed.   

Due to the uncertainty of seasonal conditions and the potential for conditions to rapidly change, the Board intends to meet regularly through the spring.  The Board retains authority granted by the IJC to deviate from Plan flows through the seasonal crest of Lake Ontario this year. Under this authority, the Board can implement additional deviations to increase flows above Plan Limits should conditions warrant. Deviations from Plan 2014 have had a very small contribution to the reduction in flood risk.  It is also important to note that deviations above Plan prescribed flows have potentially detrimental impacts to other interest groups including water users on Lake St. Lawrence and the ecosystem.

The risk of high water on Lake Ontario in 2021 remains a low possibility and is much lower than the risk was at this time last year.  However, the Board continues to emphasize that, if basin weather conditions should become extremely wet, similar to those observed in 2017 and 2019, no deviation strategy will prevent water levels that can cause flooding and damage to shoreline properties. Eliminating such damages is beyond the reach of outflow regulation and are more reliably addressed through coastal resilience and planning.

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 https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard (English), and more detailed information is available on its website at https://www.ijc.org/en/loslrb.



Rob Caldwell:              (613) 938-5864                                    Rob.Caldwell@canada.ca

Bryce Carmichael:       (513) 418-8562                                    ILOSLRB-USSection@usace.army.mil

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.  The IJC announced that the size of the Board has been reduced from 12 members to 6 members effective 1 December, 2020. The re-structured Board continues to include one member each nominated by the Government of Canada, the Government of the United States, the Province of Quebec, the Province of Ontario and the State of New York and includes one additional member on the US side to ensure equal membership from both countries. Board members continue to serve in their personal and professional capacity and consider interests of the entire Lake Ontario-St. Lawrence River system. The Board’s online membership page has been updated here to reflect this change. This re-structure does not fundamentally alter the process by which the Board makes regulatory decisions.  All 6 previous Board members are serving on an Interim Advisory Group (IAG).  The IAG continues to attend meetings and their recommendations and input on regulatory decisions is still given significant weight in the Board’s final decision making process.

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 75.92 m (249.1 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 (ijc.org/loslrb) and Facebook page (https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard).