Update: Water Levels and Current Conditions in the Lake Ontario-St. Lawrence River System

Ottawa – A wet weather system has remained over Lake Ontario-St. Lawrence River basin for several days. The jet stream is expected to finally move the weather system east by late Friday. The persistent rain and runoff from the system continue to cause water levels in Lake Ontario and the St. Lawrence River to rise. Lake levels are largely dependent on inflows received from Mother Nature, namely precipitation, which is very unpredictable more than a few days in advance.

Lake Ontario levels have been rising at a rate of approximately 1-1.5 cm (0.4-0.6 in) per day and have reached 75.32 m (247.11 ft) today while levels of the St. Lawrence River at Pointe-Claire (Montreal) have risen above 22.25 m (73 ft). Continued wet weather and runoff from the recent rains may 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.

At this time, the water levels of Lake Ontario and the St. Lawrence River are expected to remain above the long-term average but below the record highs observed in 2017 and 2019, and below the record high observed in Lake Ontario this same week in 1973 (75.71 m, 248.39 ft).

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 International Lake Ontario-St. Lawrence River Board is closely monitoring the situation. The Lake Ontario outflow into the St. Lawrence River continues to be adjusted in accordance with Plan 2014. Flow adjustments are made daily in accordance with the F limit which considers both upstream and downstream conditions.

Updates will be provided next week and as conditions change. Forecasts of Lake Ontario water levels for the next several months are updated weekly at https://ijc.org/en/loslrb/watershed/forecasts

Please continue to monitor conditions in your local area, emergency response is typically provided through your local municipality.

For more information on:

Lake Ontario Outflow Changes: https://ijc.org/en/loslrb/watershed/outflow-changes
Water levels: https://ijc.org/en/loslrb/watershed/water-levels
Plan 2014 F limit: https://ijc.org/en/loslrb/watershed/faq/4#4-8-2
Ottawa River Outflows: https://ottawariver.ca/