Shoreline Conditions Statement Extended: Lake Ontario Flood Outlook

The water level of Lake Ontario has remained stable over the past three weeks and is currently 75.41 meters above sea level (masl).

• Since the water level reached a peak on May 27th at 75.43 m, Lake Ontario levels have only fluctuated about 5cm, while inflows from precipitation and runoff have matched outflows to the St. Lawrence River.
• Water levels will begin their seasonal decline when outflows and evaporation exceed the inflows from precipitation and runoff. This will happen under normal water supplies; however, higher water levels are possible if weather and water supply conditions are wetter than average. Forecasts suggest that 10 to 20 mm of rain is possible over the next 10 days with scattered thunderstorms that could result in additional rainfall for some areas.
• Persistent precipitation this spring caused Lake Ontario water levels to increase to 75.30 m by the end of April 2026, and 75.40 m by the end of May, an increase of 86 cm since the start of March.
• The average water level in Lake Ontario rose 42 cm over the month of April, compared to the long-term average April rise of 21 cm.
• Since 1960, Lake Ontario has statistically reached at or above 75.30 m once every three years, or 33% of the years within the period of record. Although significant, reaching a water level of 75.30 m is not unusual.
• The International Lake Ontario-St. Lawrence River Board (the Board) is closely monitoring conditions and frequently adjusting Lake Ontario outflows in accordance with Regulation Plan 2014.
• If near-average water supplies are received in the basin, the lake level will start to decline over the next several weeks. Higher water levels are possible if weather and water supply conditions are wetter than average. Current forecasts indicate approximately 10 mm of rain over the next 10 days.

Heightened risks, while water levels remain above 75.30 masl, include shoreline flooding, beach submersion, and wave-driven erosion along the shoreline of Lake Ontario

This Shoreline Conditions Statement for the Lake Ontario shoreline, within the Ganaraska Region, will be in effect until Friday, July 31st, 2026, at 12 p.m. Conservation Authority staff will continue to monitor conditions and provide updates as necessary.

Note: A Shoreline Conditions Statement for Flood Outlook is an early notice indicating the potential for lakeshore flooding, erosion or hazardous conditions due to high winds, surges or rising lake levels.

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Should you have any questions or wish to report flooding, please contact the following GRCA staff (listed below) at 905.885.8173.

Mike Smith
Flood Operations Officer

Cory Harris, P.Eng.
Flood Forecasting & Warning Supervisor