Challenges of maintaining record outflow for Lake Ontario

By on June 26, 2017

At its conference call on Monday, June 19, the International Lake Ontario – St. Lawrence River Board agreed to continue efforts to further reduce high Lake Ontario levels.

The outflow from Lake Ontario was increased from 10,200 m3/s (360,200 cfs) to 10,400 m3/s (367,300 cfs) on June 14, resulting in the highest flow that has ever been continuously released from Lake Ontario for a sustained period.

St. Lawrence Seaway authorities have imposed significant limits on navigation and taken additional safety precautions for the duration of the higher flow rates.  Recreational boaters on the St. Lawrence River have also been advised of the high outflows and currents.

Water levels on the lower St. Lawrence River near Montreal have also continued to decline despite the increased outflows. Based on current observations, additional impacts of the higher flow rates are minimal.

The Board has therefore agreed to continue to release a continuous flow of 10,400 m3/s (367,300 cfs) to provide additional relief to all those affected by record-high water levels on Lake Ontario, without worsening the impacts to other stakeholders within the system.  The Board, St. Lawrence Seaway, operators of Moses-Saunders dam and navigation agencies will continue to closely monitor and evaluate the water levels, water supplies and the outflow during this period of extreme conditions.

The level of Lake Ontario has declined 11 centimeters (4.3 inches) since the peak level of 75.88 meters (248.95 feet) last recorded on May 29. Water levels downstream on the St. Lawrence River at Lake St. Louis near Montreal have declined 15 centimeters (5.9 inches) since June 12. With the weather conditions forecast over the coming days, water levels are expected to continue to fall, with the rate of decline depending on rainfall.

On June 19, Lake Ontario reached 75.77 meters (248.6 feet), 72 centimeters (28.3 inches) above its long-term average level for this time of year. The level at Lake St. Lawrence was average, while the level at Lake St. Louis hit 22.12 meters (72.6 feet), 78 centimeters (30.7 inches) above average. At Montreal Harbour, the level was 83 centimeters (32.7 inches) above average. Downstream, the flooding which has caused evacuations around Lake St. Peter is subsiding.

The Board continues to monitor the system and will confer again on June 30. Outflow changes, photos and graphs are posted to the Board’s Facebook page at and more detailed information is available on its website at .

Provided information

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