Flood Watch Issued for Lake Ontario Shoreline

The averaged Lake Ontario elevation for yesterday (Toronto, Apr-30-2019) was at 75.41 metres (m) above International Great Lakes Datum (IGLD).  Today, the lake elevation is near 75.46 m.  Flood damages in 2017 occurred at a Lake Ontario elevation of 75.45 m when waves generated during a storm event overtopped and damaged several shoreline structures.  The latest forecast (Apr-30-2019) provided by the Lake Ontario St Lawrence River (LOSLR) Board of the International Join Commission (IJC) is projecting maximum Lake Ontario elevations ranging from 75.65 to 75.95 m for late May to Early June with the upper range being 2 centimetres above the record set in 2017.  The lake damage threshold elevation of 75.45m does not account for wave generated by winds which can increase flood elevations and cause additional damages; this is especially true with onshore winds associated with storms.

Information provided by the Surface Water Monitoring Centre (SWMC) of the Ministry of Natural Resources and Forestry (MNRF) along with the IJC is indicating that rain and snow melt within the Great Lakes and St Lawrence River basin have resulted in high river and lake levels.  Major flooding is currently (Apr/May, 2019) occurring in Eastern Ontario and Quebec due to a combination of high flows in the St Lawrence and Ottawa River. 

The current Lake Erie water elevation is at a new record high for the-end-of-April.  Flows discharging from Lake Erie via the Niagara River, over the Falls, into Lake Ontario are uncontrolled.  Flows discharging out of Lake Ontario into the St Lawrence River are controlled at the Moses-Saunders (MS) Dam.  The MS Dam is operated in accordance to Plan 2014 from IJC which takes into consideration, and balances, the impacts of downstream flooding with higher Lake Ontario levels.  Over next several weeks, Lake Ontario levels will increase and will remain high for the season due to high inflows from Lake Erie and restricted Lake Ontario outflows to mitigate downstream flooding along the St Lawrence and Ottawa Rivers. 

For more information on the Lake-Ontario-St-Lawrence-River-Board and Plan-2014 please visit:


Onshore winds, especially those associated with storms systems, can generate waves resulting in shoreline erosion, flooding and damages.  Wind and wave conditions are provided by Environment Canada via the following website: 


Wind gusts at Cawthra Park in south Mississauga are available through the CVC monitoring network: 

Current Lake Ontario level is available from (add 74.2m for IGLD):


CVC will continue to monitor weather and lake conditions.  This Flood Watch will be updated by Fri-Jun-14-2019

Watercourses discharging directly into Lake Ontario may be impacted by backwater from the lake.  Residents and visitors to the Lake Ontario shoreline areas should use extreme caution and obey all closure notices for trails and pathways.  As lake levels increase, certain areas may be cut off or isolated. 

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