Drier conditions, record-high outflows starting to bring relief to Lake Ontario

A stretch of mild, dry weather has accelerated the decline in Lake Ontario water levels in recent weeks, bringing some welcome signs of relief to many of those impacted by widespread flooding and coastal damage across the Lake Ontario-St. Lawrence River basin this year. Nonetheless, high levels remain a concern and the board continues to maximize outflows with the goal of continuing to reduce Lake Ontario as quickly and safely as possible.

The board met August 31 to assess current conditions and hydrologic forecasts and review ongoing impacts of high water levels and flows throughout the Lake Ontario-St. Lawrence River system. Lake Ontario fell 35 centimeters (cm) (13.8 inches) over the past month, the greatest decline for the month of August since records began in 1918. Lake Ontario is 70 cm (27.6 in.) below the peak level recorded earlier this spring and 30 cm (11.8 in) below the highest levels previously recorded at this time of year in 1947. Outflows were 9,220 m3/s (325,600 cfs) during the last week until September 9, at midnight, when they were lowered to 8,960 m3/s (316,400 cfs). Despite the decrease, this will be a near-record outflow for this time of year, as the board continues to maximize outflows to further reduce Lake Ontario levels.

Gradual reductions in outflows will continue to be required as Lake Ontario declines in order to balance the impacts to navigation and other interests in the upper St. Lawrence River. The high outflows and falling lake levels together are continuing to cause low levels on Lake St. Lawrence (near Cornwall, Ontario and Massena, New York), the lowest at this time of year since 1998, and levels here are likely to continue declining into the fall. A short-term flow reduction scheduled over one weekend in mid-October may be considered to assist with boat haul-outs on Lake St. Lawrence. As Lake Ontario drops, this also results in increased currents and potentially hazardous navigation conditions for all in the international section of the St. Lawrence River. Further downstream, levels of Lake St. Louis (near Montreal) continue near record highs for this time of year, but remain below flood levels.

Information on hydrologic conditions, water levels and outflows are posted to the board’s Facebook page here. Additional information is available here.

Maritime Editorial