The International Lake Ontario- St. Lawrence River Board to deviate from Plan 2014 flows beginning in September to Moderate Levels on Lake St. Lawrence through Early October


The International Lake Ontario-St. Lawrence River Board will use its authority to deviate from Plan 2014 from September 2nd through October 9 to provide higher and more predictable water levels on Lake St. Lawrence and the upper St. Lawrence River.

Water levels throughout the Great Lakes have been above their long-term averages since Spring 2023.  Lake Erie and Lake Ontario began their seasonal declines in June.  The current level of Lake Ontario is 75.00 m or 246.06 ft. (17 cm or 7 in. above the long-term average) and well within the expected range for this time of year. Lake Ontario is anticipated to continue its seasonal decline and the risk of high water levels in the near future remains low. However, the above average level on Lake Ontario has triggered a threshold within Regulation Plan 2014 known as the September Rule. Plan 2014 is a set of rules that govern Lake Ontario outflows, which influence water levels across the Lake Ontario -St. Lawrence River system.

If the water levels on Lake Ontario measure above 74.8 m (245.3 ft.) at the beginning of September, the September Rule requires flow increases through Moses-Saunders Dam. The intent is that outflows will be adjusted higher to attempt to lower Lake Ontario levels to 74.8 m  by January 1st.  These conditions apply this year, and this rule would go into affect under strict application of Plan 2014.  There are three concerns with applying the September Rule:

  1. The more natural run of river that would result by not implementing the September Rule is better for the ecosystem.
  2. Based on decades of data, it has been confirmed that water levels in the fall or winter are not a good indicator of potential flooding or above average water levels the following spring and summer. 
  3. Declining water levels can indicate potential concerns for recreation on Lake St. Lawrence— a man-made lake, or forebay, between Iroquois Dam and the Moses-Saunders Dam—where outflow changes have a pronounced effect. The September Rule would cause a reduction in water levels on Lake St. Lawrence which would negatively impact some interests in the area including the recreational boating community. 

Note that adjustments to the September Rule are being considered by the Great Lakes-St. Lawrence River Adaptive Management (GLAM) Committee as part of the expedited review of Plan 2014.

The International Lake Ontario-St. Lawrence River Board has evaluated implementing a deviation from the September Rule.  Beginning on September 2, 2023, the Board will use its authority to deviate from Plan 2014 by ignoring the September Rule and thereby provide higher, more favorable water levels for interests on Lake St. Lawrence. The Board plans to negate the impacts of the deviation by year’s end by increasing flows starting in mid-October. 

This deviation foregoes the need for another flow reduction to facilitate the boat haul out in early October. The Board has purposefully decided to deviate from the September Rule through October 9 to provide higher and more predictable water levels on Lake St. Lawrence and the upper St. Lawrence River through what is typically the end of the recreational boating season.  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.

It should also be noted that although water levels within the system this summer have been generally favorable for recreational boating, this is not a result of any specific intentional strategy enacted by the regulation plan or by the Board.  Rather these favorable levels have largely been due to the weather conditions occurring this year within the system.  Not all years will have such favorable weather  conditions allowing for good water levels for recreational boating that Mother Nature provided this year.

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The International Lake Ontario-St. Lawrence River Board ensures that outflows from Lake Ontario meet the requirements of the International Joint Commission's Orders of Approval. Under any regulation plan, the ability to regulate the outflow from Lake Ontario does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes, precipitation, evaporation, and runoff cannot be controlled, and are difficult to accurately predict.