International Lake Ontario - St. Lawrence River Board

Board will reduce Lake Ontario outflows to assist with boat haul-out from Lake St. Lawrence


The International St. Lawrence River Board of Control (Board) will reduce outflows beginning on October 10 in efforts to temporarily raise water levels and assist with end-of-season boat haul out in Lake St. Lawrence.

Lake St. Lawrence is immediately upstream of the Moses-Saunders Dam at Cornwall, Ontario, and Massena, N.Y.  Decreasing the outflow through the dam has the effect of raising the water level on Lake St. Lawrence, while increasing the outflow lowers the water level.

Relatively high outflows have been prescribed by the Board in recent weeks in response to relatively high levels on Lake Ontario following a wet summer, and in accordance with the regulation plan for Lake Ontario, Plan 1958-D.  In determining the outflow, the regulation plan incorporates a number of factors, including climate conditions and water levels on Lake Ontario, inflows from Lake Erie through the Niagara River, and water level conditions on the St. Lawrence River upstream and downstream of the dam. 

Conditions across the Lake Ontario – St. Lawrence River system for this time of year make it possible for the Board to reduce outflows below Plan-specified amounts for up to 48 hours starting on October 10.  This reduction in outflows is expected to temporarily raise levels upstream of Moses-Saunders Dam by up to approximately 70 centimetres (28 inches).  Additional factors, notably winds, may result in a greater or lesser increase than predicted.

Note that further upstream, the effects of the outflow reduction on water levels will be less than near the dam. On Lake Ontario, the impact will be an increase in water level of up to 1 centimetre (0.4 inches). The Board is taking actions to minimize impacts downstream as well.

Lake Ontario is currently above its long-term average level for this time of year. The level on October 5 was 74.74 metres (245.2 feet), 10 centimetres (4.0 inches) above average. This is well within Lake Ontario’s 1.22-metre (four-foot) range, being 63 centimetres (24.8 inches) below the lake’s upper limit, and 59 centimetres (23.2 inches) above the lake’s lower limit.  The level at Lake St. Lawrence was about 44 centimetres (17.0 inches) below average.  Downstream, the level at Lake St. Louis was 2 centimetres (0.8 inches) above average; at Montreal Harbour, the level was 21 centimetres (8.0 inches) below average.

The Board, in conjunction with its staff, continues to monitor the system.  Outflow changes are posted to the Board’s Facebook page at (English) and on its website at under the Maps and Data tab, and Lake Ontario outflow changes subheading.


Gail R. Faveri: (905) 336-6007;

Arun Heer: (513) 684-6202;


The Board specifies the outflows from Lake Ontario, generally according to Plan 1958-D as required in the Orders from the International Joint Commission. This plan was agreed to by the United States and Canada when the dam was constructed. Our website contains much useful information including a Frequently Asked Questions section under the News and Information tab that will further explain the details of Plan 1958-D and our Board.  In order to know what outflows to specify, the Board, in conjunction with its staff, pays close attention to water levels in the Lake Ontario-St. Lawrence River system and the upstream Great Lakes.  The Board is thus prepared to take action when applicable.  Outflow changes are posted to the Board’s Facebook site at and its website at under the Maps and Data tab, Lake Ontario outflow changes subheading.

Water levels on both Lake Ontario and the St. Lawrence River vary considerably from year-to-year depending on the weather conditions. The Board urges everyone to be prepared to live within the full range of levels that have occurred.   Although the Board strives to maintain the range of monthly mean levels of Lake Ontario below the upper limit of 75.37 metres (247.3 feet) and above the lower limit (from April through November) of 74.15 metres (243.3 feet) specified in the Orders of Approval, since regulation began in 1960, actual monthly levels have ranged from a high of 75.73 metres (248.5 feet.) to a low of 73.82 metres (242.2 feet) due to climate conditions outside the design range.  Levels on the river tend to vary more widely.  Furthermore, excessive wind set up and wave action may significantly increase or decrease local levels on both the lake and river.  Strong winds can change water levels temporarily by over half a metre (two feet) in some locations.

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