Current Water Level Conditions and Lake Ontario Water Supplies

The International Lake Ontario-St. Lawrence River Board (the board) continues to monitor conditions in Lake Ontario and the St. Lawrence River:

• Continued rainfall and runoff may result in flooding of vulnerable areas along the Lake Ontario shoreline as well as downstream along the St. Lawrence River, including the Montreal archipelago and Lake St. Pierre.
• Water levels of Lake Ontario and the St. Lawrence River (Lake Ontario: 75.37 metres or 247.28 feet; Pointe-Claire: 21.91 metres or 71.88 feet) remain above long-term (1960-2025) average but well below the record high for this week, i.e., 75.85 meters or 248.85 feet, that occurred in 2017.
• Lake Ontario outflows will continue to be set in accordance with the rules of Regulation Plan 2014. The board may deviate from these prescribed flows if criterion H14 Lake Ontario levels are met, and the board determines that deviations are warranted. Criterion H14 trigger water levels vary through the year. The current upper H14 trigger level is 75.60 metres (248.00 feet).
• If weather conditions are near average, Lake Ontario is expected to reach a seasonal peak of approximately 75.40 metres (247.37 feet) in May or June. However, higher water levels are possible if weather conditions are much wetter than average. Long-term water levels are difficult to predict, much like weather forecasts.
• Strong winds, when coupled with even moderately-high water levels, can result in localized 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.

There has been persistent precipitation throughout the Lake Ontario and St. Lawrence River basin this spring. The Ottawa River, which meets the St. Lawrence River at Montreal, discharged around 7,740 cubic metres per second (m³/s) or 273,300 cubic feet per second (ft³/s) into the lower St. Lawrence River on April 22. This is approximately three times the amount of water that flowed over Niagara Falls (2,600 m³/s or 91,800 ft³/s) that same day. To add to that, Rochester, NY, recorded its wettest March and April in 153 years.

Due to this persistent precipitation and high Ottawa River flows, frequent Lake Ontario outflow adjustments were made between April 16 and May 6 in accordance with the F limit, which aims to balance risks and impacts associated with flooding both upstream and downstream of the Moses-Saunders Power Dam. [The F limit sets maximum outflows from Lake Ontario based on the level of Lake St. Louis (measured at Pointe Claire) to limit downstream flooding in consideration of Lake Ontario levels.] Since then, Ottawa River outflows have declined, enabling the Lake Ontario outflow to increase. As of May 7, the Lake Ontario outflow has been set in accordance with the Plan 2014 applicable Rule Curve flow and is no longer restricted by the F limit.

While the board regulates outflows from Lake Ontario, regulation cannot eliminate the recurrence or negative effects of extremely wet or dry water supplies on water levels. These water supplies and processes are uncontrolled; most of the water coming into Lake Ontario comes from Lake Erie, while remaining water comes from precipitation, runoff and evaporation, in the basin.

Community members should continue to monitor conditions in their local area. Emergency planning and response are typically provided through local municipalities.

For more information:

• Water levels (updated every weekday): https://ijc.org/en/loslrb/watershed/water-levels
• Flows (updated every weekday): https://ijc.org/en/loslrb/watershed/flows
• Lake Ontario forecast (updated on Thursdays): https://ijc.org/en/loslrb/watershed/forecasts
• Lake Ontario outflow changes (updated in real time as flow changes occur): https://ijc.org/en/loslrb/watershed/outflow-changes#flow_table
• Plan 2014 F limit: https://ijc.org/en/loslrb/watershed/faq/4#4-8-2
• Criterion H14 triggers authorizing deviations: https://ijc.org/en/loslrb/watershed/faq/4#4-8-1
• Ottawa River conditions and forecast (updated daily during freshet): https://ottawariver.ca/
• ILOSLRB video on balance upstream and downstream conditions: https://www.ijc.org/en/loslrb/videos or https://www.youtube.com/watch?v=v_AOC_CNa3Y

Contacts:

Canada: [email protected]

United States: [email protected]

The International Lake Ontario-St. Lawrence River Board ensures that outflows from Lake Ontario meet the requirements of the International Joint Commission's Orders of Approval. Under any regulation plan, the ability to regulate the outflow from Lake Ontario does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes, precipitation, evaporation, and runoff cannot be controlled, and are difficult to accurately predict.