GRCA Issues Flood Warning – Lake Ontario Shoreline

Flood Potential: High

The Ganaraska Region Conservation Authority advises that water levels on Lake Ontario have risen to 75.68 meters above sea level, which is 64 cm above average and 20 cm below the peak water level of the 2017 flood event. The Flood Watch issued on May 6th is therefore upgraded to a Flood Warning for the Lake Ontario shoreline.

With flooding ongoing on the Ottawa and St. Lawrence Rivers, outflows from Lake Ontario have been temporarily reduced to balance impacts both downstream and upstream. Outflows will be gradually increased again as downstream flooding subsides. The International Lake Ontario – St. Lawrence River Board predicts that Lake Ontario will peak in the last week of May or the first week of June at 75.74 meters above sea level, which is below the extreme highs of 2017. Heavy rainfall over the Lake Ontario or Ottawa River watersheds could push water levels higher.

Very high inflows from the Niagara River have contributed to persistently high Lake Ontario water levels and high flows on the St. Lawrence River. This means that even when outflows are increased to the maximum, water levels will decline slowly and take several weeks or months to bring them down to within a normal range.

The main concern during high lake levels is shoreline erosion and flooding of low-lying shorelines including dynamic beaches and wetlands along the shore. Shortened beaches, waterfront trails and shoreline protections may be damaged by wave action especially during strong winds from the south.

Water levels and flows on local streams and on Rice Lake are returning to normal spring levels. This Flood Warning is issue for the shoreline of Lake Ontario only.

Water levels on Rice Lake have peaked and are declining a few centimeters every day. The current water level is 187.08 meters above sea level, which is approximately 30 cm above the summer navigation level. The risk of shoreline flooding on Rice Lake has passed and the Flood Watch issued on May 6th is cancelled.

While this Flood Warning is in effect, shorelines may be slippery with unstable banks and bluffs may be actively eroding. Residents are asked to exercise caution around our shorelines and to alert any children in their care of these dangers.

This Flood Warning for the Lake Ontario shoreline will be in effect through Monday, June 3rd, 2019. Conservation Authority staff will continue to monitor conditions, and provide updates as necessary. Should you have any questions or wish to report flooding, please contact the following GRCA staff at 905-885-8173.

Mike Smith                                                     
Flood Operations Officer                              

Note: A Flood Warning is issued as notice that flooding is imminent or already occurring in specific watercourses or municipalities.