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International Lake Ontario – St. Lawrence River Board Continues to Assess Current and Forecast Water Levels on Lake Ontario and the St. Lawrence River

Ottawa – Lake Ontario is currently 34 cm (13.4 inches) above the long-term average (1918-2020) and 34 cm (13.4 inches) below the record high set in 1945 for this time of the year. In terms of total water supply to Lake Ontario, September through November 2021 was the third wettest fall on record. As a result, Lake Ontario experienced the third-largest rise in water levels in October. The lake rose 8 cm (3.1 inches) as opposed to decreasing an average of 11 cm (4.3 inches) typically experienced that time of year.

November outflows were the 6th highest on record while Lake Ontario water levels were the 13th highest.  Lake Ontario rose 3 cm (1.2 inches) from the beginning of September through the beginning of December, while the average seasonal change is a decline of 29 cm (11.4 inches). The International Lake Ontario-St. Lawrence River Board (“ILOSLRB” or “Board”) continues to maintain increased outflows through the Moses-Saunders Dam to return the water level of Lake Ontario to the level it would be currently if outflow deviations had not been made earlier this year. Those earlier deviations below plan flows were made when the region was experiencing drought conditions early this summer. The ongoing offsetting deviations above plan flows are expected to be completed over the next few weeks.

Currently, the regulation plan is prescribing very high outflows, the third-highest on record for this time in December, and these plan flows are higher than in December 2020.   The regulation plan will continue to prescribe high outflows over the winter.

“Water levels of the Great Lakes cannot be fully controlled through adjustment of outflows, nor can outflow adjustments eliminate the risk of extreme water levels occurring during periods of very wet and/or very dry water supply conditions”, said Mr. David Harper, Canadian Co-Chair of the ILOSLRB. There is an unpredictable natural supply of water for the Great Lakes and it is important to recognize the full range of high and low water levels that have historically occurred within the system and may occur again in the future. “Great Lakes States and Provinces, in partnership with government and non-government agencies, and property owners, should continue to focus on resiliency strategies to respond to the wide range of naturally occurring water levels we continue to experience in the Great Lakes”, said Mr. Steve Durrett, United States Co-Chair of the ILOSLRB.

The Board will continue to closely monitor weather forecasts, La Niña, and water supply conditions, and will evaluate the outflow strategy regularly. It is very important to note that there is little correlation between December water levels and spring water levels. Current water levels are not an accurate indicator of what actual conditions will be in three to six months. For example, in December 2019 water levels were 13 cm (5.1 inches) higher than they are now and there was no significant lakeshore flooding in the spring of 2020; the peak lake level in 2020 was 75.40 m (247.4 ft). Weather forecasts are not reliable more than a few weeks into the future and cannot accurately tell us what the regional ice formation and snowfall will be for the winter, or how much rainfall might occur this coming spring.

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, and more detailed information is available on the website at https://www.ijc.org/en/loslrb. Frequently asked questions are available at https://ijc.org/en/loslrb/watershed/faq/4.