Lake Ontario-St. Lawrence River Water Levels Update – Autumn 2024

Ottawa – The International Lake Ontario-St. Lawrence River Board is providing this notice to summarize the water level conditions from September 2024 through the remainder of Autumn.

Plan 2014 is a set of rules that govern Lake Ontario outflows through the Moses-Saunders Dam located near Massena, New York and Cornwall, Ontario. 

Water supply conditions have resulted in one of the longest periods of sustained near-long-term average water levels on Lake Ontario.

1. The International Lake Ontario-St. Lawrence River Board used its authority under its minor deviation directive, to deviate from the rules of Plan 2014 on three occasions this fall. The cumulative effect of these minor deviations is equivalent to +0.5 cm (+0.2 in) of water on Lake Ontario relative to if the deviation had not occurred.
2. 1. As described in the news release on August 29, 2024, the Board’s strategy was to adjust flows when necessary from September 1 through October 18 to target a minimum weekly mean water level of Lake St. Lawrence of 73.1 m (239.8 ft) to provide more predictable water levels on Lake St. Lawrence and the upper St. Lawrence River. The deviation was only needed the week of September 28 through October 4 when 60 m³/s below the flow prescribed by Plan 2014 Rule Curve was released.
   2. The Board implemented two other minor deviations at the request of hydropower entities for a 12-hour period on September 4 (net effect of 80 m³/s below the flows prescribed by Plan 2014 Rule Curve for the week of August 31 through September 6) and a 12-hour period on September 24 (net effect of 30 m³/s below the flows prescribed by Plan 2014 Rule Curve for the week of September 21 through 27). Flows during these periods were temporarily reduced to enable safe conditions for in-water work at dam facilities.

1. As required by the IJC’s Directive, minor deviations must be restored by equivalent offsetting deviations from the plan flow. In this case, outflows through the dam will be increased above the flows prescribed by Plan 2014 Rule Curve for a two-week period.
   1. The week of October 19 through 25 the outflow was set at 7,090 m³/s which is 90 m³/s higher than the Rule Curve flow prescribed by Plan 2014.
   2. The week of October 26 through November 1 the outflow will be set at 7,060 m³/s which is 80 m³/s higher than the Rule Curve flow prescribed by Plan 2014.
   3. The higher flow, relative to Plan 2014, has the effect of accelerating the seasonal decline of water levels upstream of the Moses-Saunders Dam on Lake St. Lawrence by approximately 3-4 cm (1-1.5 in) and removing the +0.5 cm (+0.2 in) of water temporarily stored on Lake Ontario from the earlier deviations. As water levels throughout the system continue their gradual seasonal decline, the Board encourages recreational boaters to monitor the water level forecasts to determine the optimal time to remove their vessels and equipment for the season.

For more information on:

• Lake Ontario Outflow Changes: https://ijc.org/en/loslrb/watershed/outflow-changes
• Water Levels: https://ijc.org/en/loslrb/watershed/water-levels
• Water Level Forecast: https://ijc.org/en/loslrb/watershed/forecasts