Lake Ontario Outflow Changes

The outflow target for the week of April 19 through April 25 is the applicable Rule Curve flow of 7,210 m³/s.

Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit. For information on current conditions in the Ottawa River basin, please visit Ottawa River Regulation Planning Board - Ottawa River Regulation Planning Board

The outflow target for the week of April 12 through April 18 is the applicable Rule Curve flow of 7,200 m³/s.

Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit. For information on current conditions in the Ottawa River basin, please visit Ottawa River Regulation Planning Board - Ottawa River Regulation Planning Board

The outflow target for the week of April 5 through April 11 is the applicable Rule Curve flow of 7,090 m³/s.

Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit. For information on current conditions in the Ottawa River basin, please visit Ottawa River Regulation Planning Board - Ottawa River Regulation Planning Board

The outflow target for the week of March 29 through April 4 is the applicable Rule Curve flow of 6,930 m³/s.

Flows along the Ottawa River have begun increasing due to spring runoff. Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit.

The ice covers on Lake St. Lawrence and in the Beauharnois Canal began melting in the past week because of the warm temperatures and rainfall. There is a small amount of ice remaining upstream of the Moses-Saunders Dam and a few km of ice remaining in the Beauharnois Canal.

The outflow target for the week of March 22 through March 28 is the applicable Rule Curve flow of 6,900 m³/s.

Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit (https://ijc.org/en/loslrb/watershed/faq/4#4-8-2). Since the level of Lake Ontario is below 75.3 m, the first F-limit tier applies and the outflow would be adjusted to maintain a maximum level of 22.10 m at Lake St. Louis (measured at Pointe Claire).

 From Table B4 of the Plan 2014 Compendium:

The outflow target for the week of March 15 through March 21 is the applicable Rule Curve flow of 6,660 m³/s.

The outflow target for the week of March 8 through March 14 is the applicable Rule Curve flow of 6,560 m³/s.

As previously noted on February 20, the Lake Ontario outflow was temporarily reduced to 6,230 m³/s on February 17 and to 6,000 m³/s on February 18, in accordance with the Plan 2014 I Limit. As conditions improved, the outflow was gradually increased to 6,100 m³/s on February 20, to 6,300 m³/s February 21, and returned to the applicable Rule Curve flow of 6,540 m³/s on February 22. 

The outflow target for the week of March 1 through March 7 is the applicable Rule Curve flow of 6,420 m³/s.

On February 17, following a significant snowstorm and strong winds, the Lake Ontario outflow was reduced to 6,230 m³/s, in accordance with the Plan 2014 I Limit, to promote the stability of the ice covers in the Beauharnois Canal and Lake St. Lawrence. However, the ice conditions did not stabilize and the outflow was further reduced to 6,000 m³/s on February 18. As conditions improved, the Lake Ontario outflow was increased to 6,100 m³/s on February 20. It is expected that the outflow will continue to be gradually increased in the coming days. The outflow target for the week of February 22 through February 28 is the applicable Rule Curve flow of 6,540 m³/s.

The outflow target for the week of February 15 through February 21 is the applicable Rule Curve flow of 6,520 m³/s.

In the remaining weeks of winter, the outflow may 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.

The outflow target for the week of February 8 through February 14 is the applicable Rule Curve flow of 6,560 m³/s.

On February 1, during a period of colder temperatures, the Lake Ontario outflow was reduced to 6,230 m³/s, in accordance with the Plan 2014 I Limit, to promote the formation and stability of the ice cover on Lake St. Lawrence. On February 3, as ice conditions improved, the Lake Ontario outflow was increased to the Rule Curve flow of 6,610 m³/s.

If colder temperatures return, the Lake Ontario outflow may be operationally adjusted again in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of the ice covers in the Beauharnois Canal and on Lake St. Lawrence.

The outflow target for the week of February 1 through February 7 is the applicable Rule Curve flow of 6,610 m³/s.  

On January 27, during a period of colder temperatures and very strong winds, the Lake Ontario outflow was reduced to 6,230 m³/s, in accordance with the Plan 2014 I Limit, to promote the formation and stability of the ice covers in the Beauharnois Canal and on Lake St. Lawrence. On January 28, as ice conditions improved, the Lake Ontario outflow was increased to the Rule Curve flow of 6,720 m³/s.

If colder temperatures return, the Lake Ontario outflow may be operationally adjusted again in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of the ice covers in the Beauharnois Canal and on Lake St. Lawrence.

The outflow target for the week of January 25 through January 31 is the applicable Rule Curve flow of 6,720 m³/s.  

Ice-building temperatures returned on January 19 and the Lake Ontario outflow was reduced to 6,230 m³/s in accordance with the Plan 2014 I Limit. An additional 2 km of ice, for a total of 16 km, has accumulated in the Beauharnois Canal and a partial ice cover has formed immediately upstream of the Moses-Saunders Dam. The Lake Ontario outflow was increased to 6,530 m³/s on January 22 and to 6,720 m³/s on January 23. 

If colder temperatures return, the Lake Ontario outflow may be operationally adjusted again 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. 

The outflow target for the week of January 18 through January 24 is the applicable Rule Curve flow of 6,760 m³/s. However, the Lake Ontario outflow will continue to 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 January 7, slushy ice slowly began to accumulate in the Beauharnois Canal. On January 9, strong winds caused the ice to move, and the Lake Ontario outflow (at Moses-Saunders Dam) was reduced to 6,260 m³/s with the goal of stabilizing the ice cover. However, the ice cover did not stabilize and the Lake Ontario outflow was then further reduced to 5,700 m³/s. As ice conditions improved, the Lake Ontario outflow was gradually increased on January 11, 12, and 13, and was set to the Rule Curve flow of 6,800 m³/s at noon on January 15.

Approximately 14 km of ice has accumulated in the Beauharnois Canal. A significant ice cover has not yet formed on Lake St. Lawrence upstream of the Moses-Saunders Dam. It is expected that the outflow will need to be decreased again next week when colder temperatures return.

The outflow target for the week of January 11 through January 17 is the applicable Rule Curve flow of 6,800 m³/s. However, the Lake Ontario outflow has been reduced to 6,260 m³/s to promote the formation of an ice cover in the Beauharnois Canal. 

During the winter months, 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 ice covers in the Beauharnois Canal and on Lake St. Lawrence.

For more information,

• FAQ 2.7 “What actions does the Board take to manage ice conditions in the St. Lawrence River during the winter?”: https://ijc.org/en/loslrb/watershed/faq/2#2-7
• FAQ 4.8.4 “What is the I Limit?”: https://ijc.org/en/loslrb/watershed/faq/4#4-8-4
• This video demonstrates the importance of ice management in the St. Lawrence River: https://vimeo.com/168823489
• This video discusses winter operations under Plan 2014: https://vimeo.com/670845537

The outflow target for the week of January 4 through January 10 is the applicable Rule Curve flow of 6,820 m³/s.

The outflow target for the week of December 28, 2024 through January 3, 2025 is the applicable Rule Curve flow of 6,780 m³/s.