Following the end of navigation season on December 31, 2019, Lake Ontario outflows were increased as much as possible and will remain until ice formation resumes on the St. Lawrence River. The exact amount of the flow increase depends on ice and water level conditions in the St. Lawrence River. Water levels downstream of the Moses-Saunders Dam, including around the Montreal area, are expected to rise, but will be monitored closely to ensure they are maintained below flood levels.
Lake Ontario outflows were first set to record-rates in June as water levels of Lake Ontario reached a new daily record-high of 249.08 feet. This followed an unprecedented spring that saw record water levels and flows occurring across the Great Lakes and Ottawa River basins. High outflows from Lake Ontario continued through the summer, fall, and early winter, resulting in more water released from Lake Ontario during the last seven months of 2019 than in any year since the start of records in 1900. The average outflow from June through December was 337,600 cubic feet per second, the highest flow ever released over this period, and equivalent to removing nearly 30 feet of water from Lake Ontario during this time.
However, with all of the Great Lakes seeing record or near-record water levels in 2019, inflows to Lake Ontario have also remained high during that time. Lake Ontario’s level was 246.06 feet on December 29, 2019 and remains well-above seasonal averages. High inflows are expected to continue into 2020.
The International Lake Ontario – St. Lawrence River Board, under authority granted to it by the International Joint Commission, will continue to deviate from Plan 2014 and will look for any and all opportunities to remove additional water from Lake Ontario prior to the spring.
The Board, in conjunction with its staff, continues to monitor conditions on an ongoing basis. Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the board’s website https://www.ijc.org/en/loslrb.
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