Maximum outflow for Lake Ontario continuing to relieve high water

Several months of maximizing outflows has dropped Lake Ontario at an unprecedented rate, well below the record peak set last May, water levels remain relatively high for this time of year. Outflows continue to be maximized in response while making intermittent and temporary reductions to manage challenging ice conditions in several areas of the St. Lawrence River. 

Following last year’s record wet spring, and despite several months of continuing wet weather, Lake Ontario’s level had fallen 1.12 meters (3.7 feet) below its 2017 peak, as of the start of January. Extreme cold and snow near the start of 2018 followed by milder temperatures, heavy rain and snowmelt more recently has Lake Ontario’s level rising again.

In response to the high water levels, the International Lake Ontario-St. Lawrence River Board is still setting outflows from Lake Ontario at the highest rates. Recent reductions were required to promote the formation of a solid, stable ice cover in critical sections of the St. Lawrence River, allowing increased outflow under the ice. Without this stable ice cover, the risk of ice jams is high. These ice jams can clog the river, forcing sudden, significant flow reductions and an increased risk of localized flooding. Outflows are currently 1,730 cubic meters per second above average, 180 cubic meters per second above the previous record-high flow in 1986 and are expected to continue to increase gradually as ice and weather conditions allow. 

While Lake Ontario remains well above average, historically, winter water levels have not provided an accurate indicator of the peak later in spring. Hydrologic conditions have a much greater influence, and while impossible to predict, it is unlikely that last spring’s combination of exceptional rainfall, snowmelt and rapidly rising inflows from Lake Erie will all repeat themselves and lead to extremely high water levels again this year. Nonetheless, extreme conditions may occur in any given year, and when they do, the risk of extreme water levels cannot be substantially reduced through regulation of outflows. 

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 here (English), including this video, which explains why the management of ice conditions on the river is so critical. 

Maritime Editorial