Lake Ontario Outflow Changes

The outflow target for the week of February 14 through February 20 is the applicable Rule Curve flow of 6,260 m³/s, as prescribed by Plan 2014. 

The ice cover in the Beauharnois Canal and the St. Lawrence River are currently stable. However, if conditions require, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit to promote the stability of the ice covers and to maintain the water level of Lake St. Lawrence (measured at Long Sault Dam) near or above 71.8 m to protect municipal water intakes.

The outflow target for the week of February 7 through February 13 is the applicable Rule Curve flow of 6,290 m³/s, as prescribed by Plan 2014. 

The ice cover in the Beauharnois Canal and the St. Lawrence River are currently stable. However, if conditions require, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit to promote the stability of the ice covers and to maintain the water level of Lake St. Lawrence (measured at Long Sault Dam) near or above 71.8 m to protect municipal water intakes.

The ice cover in the International Section of the St. Lawrence River has progressed upstream of Iroquois Dam and is currently stable, which allowed the Lake Ontario outflow to be gradually increased on January 27 and January 28 in accordance with the Plan 2014 I Limit. The ice cover in the Beauharnois Canal also remains stable.

The outflow target for the week of January 31 through February 6 is the applicable Rule Curve flow of 6,370 m³/s, as prescribed by Plan 2014. If conditions require, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit to promote the stability of the ice covers and to maintain the water level of Lake St. Lawrence (measured at Long Sault Dam) near or above 71.8 m to protect municipal water intakes.

The outflow target for the week of January 24 through 30 is the applicable Rule Curve flow of 6,490 m³/s, as prescribed by Plan 2014. However, on January 23 the outflow will be reduced to 6,230 m³/s in accordance with the I Limit to promote the progression of the ice cover in the upper St. Lawrence River between Morrisburg, ON and Iroquois, ON. The ice cover in the Beauharnois Canal is currently stable.

In the coming week, the outflow will continue to be operationally adjusted in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of the ice covers on Lake St. Lawrence and in the Beauharnois Canal.

The outflow target for the week of January 17 through 23 is the applicable Rule Curve flow of 6,470 m³/s, as prescribed by Plan 2014. If the current flow of 6,240 m³/s remains unchanged today and tomorrow (January 15 and 16), the remaining accumulated minor deviation that was conducted for Lake St. Louis recreational boat haul-out on October 17 will be fully offset by the end of this week (January 16).    

Ice covers remain in the Beauharnois Canal and Lake St. Lawrence but have receded following recent warm temperatures. With the return of colder temperatures, the outflow may need to be operationally adjusted in accordance with the I Limit to promote the stability and potential additional progression of the ice covers. 

Given current conditions in the Ottawa River and the lower St. Lawrence River, operational adjustments in accordance with the M Limit are not expected to be required in the coming weeks. The water level of Lake St. Louis (measured at Pointe Claire) is approximately 20 cm above the applicable M-Limit tier of 20.64 m. 

The outflow target for the week of January 10 through 16 is 6,240 m³/s, which is 60 m³/s below the Rule Curve flow prescribed by Plan 2014. A slightly lower outflow will be released to offset the minor deviation that was conducted for Lake St. Louis recreational boat haul-out on October 17-18, 2025.  

However, if conditions require, the outflow will be operationally adjusted in accordance with the I Limit and/or the M Limit. 

• There are partial ice covers in Beauharnois Canal and on Lake St. Lawrence upstream of the Moses-Saunders Dam. If needed, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit, to promote the formation and stability of the ice covers.
• Since the level of Lake Ontario is above 74.2 m, the first tier of the M Limit applies, and if needed, the outflow would be adjusted to maintain a minimum level of 20.64 m at Lake St. Louis (measured at Pointe Claire).

The Lake Ontario outflow was operationally adjusted several times between December 26 and December 31 in accordance with the Plan 2014 M Limit. On January 1, 2026, the outflow was decreased to the applicable Rule Curve flow of 6,100 m³/s.

The outflow target for the week of January 3 through January 9, 2026 is 6,170 m³/s, which is 50 m³/s below the Rule Curve flow prescribed by Plan 2014. A slightly lower outflow will be released to offset the minor deviation that was conducted for Lake St. Louis recreational boat haul-out on October 17-18, 2025.  

However, if conditions require, the outflow will be operationally adjusted in accordance with the M Limit.  Since the level of Lake Ontario is above 74.2 m, the first tier of the M Limit applies, and the outflow will be adjusted to maintain a minimum level of 20.64 m at Lake St. Louis (measured at Pointe Claire).

Additionally, during the winter months, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of ice covers in the Beauharnois Canal and on Lake St. Lawrence.

On Tuesday, December 23, the Lake Ontario outflow was operationally adjusted from 6,500 m³/s to 6,400 m³/s in accordance with the Plan 2014 M Limit. 

The Rule Curve flow for the week of December 27 through January 2 is 6,100 m³/s. However, the outflow will continue to be set in accordance with the M Limit to start the week.  Since the level of Lake Ontario is above 74.2 m, the first tier of the M Limit applies, and the outflow will be adjusted to maintain a minimum level of 20.64 m at Lake St. Louis (measured at Pointe Claire). 

During the winter months, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of ice covers in the Beauharnois Canal and on Lake St. Lawrence. 

As required by the IJC’s Directive, the small amount of additional water (0.34 cm or 0.1 inch) that was released from Lake Ontario during the temporary outflow increase (minor deviation) on October 17 and 18 will be completely restored as conditions permit.