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With Lake Ontario water levels declining, IJC reduces outflows

Photo by Tom Rivers: A boater is out on Lake Ontario near Point Breeze in this file photo from June 30, 2016.

Posted 2 June 2020 at 2:43 pm

Press Release, International Joint Commission

Lake Ontario levels peaked early this year at 247.38 feet on May 5, which was 4 inches below the general flood stage and 20 inches lower than the peak in 2019.

Lake levels are expected to continue their seasonal decline through summer, and have fallen 2 inches from the crest to date.

Lower Lake Ontario levels and the continuing high outflows are causing increased currents in the upper St. Lawrence River and also extremely low levels on Lake St. Lawrence, the forebay just upstream of the Moses-Saunders Power Dam. The International Lake Ontario – St. Lawrence River Board has assessed the situation carefully and, if necessary, will act to augment low levels at this location over the coming weeks.

The Board’s extended general deviation authority (as granted by the International Joint Commission on October 9, 2019) has ended. The Board is no longer deviating by releasing outflows above Plan 2014 prescribed flows, since Lake Ontario reached its peak and began its seasonal decline.

The peak level of Lake Ontario is still well above average, but was reduced by 7 inches owing to deviations from Plan 2014. These deviation totals accumulated over the past several months as the Board attempted to remove as much water as possible from Lake Ontario, prior to spring.

Drier conditions have prevailed in recent weeks, including around Lake Ontario and in the Ottawa and lower St. Lawrence River basins. These are the primary reasons for the recent decline in Lake Ontario levels, which has occurred despite very high inflows from the extremely high upper Great Lakes. These high inflows will continue for the foreseeable future and, in response, Plan 2014 will continue to prescribe very high outflows, which will enhance Lake Ontario’s seasonal decline.

However, the lower and declining levels on Lake Ontario combined with the high outflows through the Moses-Saunders Power Dam that will continue are resulting in very low levels on Lake St. Lawrence that are anticipated to persist for months to come.

This will be the fourth straight summer of well-below-average levels of Lake St. Lawrence, which responds much more rapidly and significantly to increases in outflows than the much larger Lake Ontario upstream. Had the Board not deviated and removed water from Lake Ontario since last spring, Lake St. Lawrence would currently be approximately 6 inches higher.

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