Recent wet weather impacting Lake Ontario water levels
May 7—Lake Ontario water levels are expected to remain above long-term average but below the record-highs observed in 2017 and 2019, according to the International Lake Ontario-St. Lawrence River Board.
Persistent rain and runoff from last week's wet weather system caused water levels in Lake Ontario and the St. Lawrence River to rise. The precipitation was about 40% above average, the board noted.
Lake Ontario levels have been rising at a rate of approximately 0.4-0.6 inches per day and had reached 247.21 feet as of Friday while levels of the St. Lawrence River at Pointe-Claire (Montreal) have risen above 73 feet.
Additional wet weather and runoff could result in flooding of vulnerable areas along the Lake Ontario shoreline as well as downstream along the St. Lawrence River, including Lake St. Louis and Lake St. Pierre.
In addition to increased runoff into Lake Ontario, outflows from the Ottawa River and other tributaries into the St. Lawrence River have increased substantially in the past several days due to the widespread major rainfall. The Lake Ontario outflow into the St. Lawrence River continues to be adjusted in accordance with Plan 2014. Flow adjustments are made daily with consideration to both upstream and downstream conditions.
Forecasts of Lake Ontario water levels for the next several months are updated weekly at https://ijc.org/en/loslrb/watershed/forecasts.