International Lake Ontario - St. Lawrence River Board

Board decides to continue releasing Plan 1958-D flows


The International St. Lawrence River Board of Control (Board) recently reviewed conditions in theLakeOntario-St.Lawrence River system and has agreed to continue releasing outflows in accordance with the regulation plan, Plan 1958-D.  Earlier this year, when Lake Ontario was low and water supply conditions dry, the Board retained 2.8 cm (1.1 in) of water to meet future critical needs.  About 2.7 cm (1.1 in) of this water remains.  The Board plans to meet in late October to discuss when and how quickly to release the stored water.  

After starting the year well below average, and peaking in July above average, Lake Ontario is currently in its normal seasonal decline.  The water level on September 17 was 74.76 m (245.28 ft), at the middle of Lake Ontario’s 1.22 m (4 ft) range, being 61 cm (24 in) from its upper and lower limits.  The level is about 5 cm (1.9 in) above long-term average for this time of year.  Lake St. Lawrence, just upstream of the Moses-Saunders powerhouse, is above average.  Downstream, the levels at Pte. Claire on Lac St-Louis are about 11 cm (4.3 in) and at the Montreal Harbour 29 cm (11.4 in) below average. 

The Board’s strategy will allow it to address uncertainty in the water supplies and levels between now and the seasonal close of navigation upstream of Montreal.  The Board strategy also allows for varying the outflow to meet critical conditions in the river.  The Board, in conjunction with its staff, continues to monitor the situation closely and is prepared to take further action as required.  Outflow changes are posted to the Board’s Facebook site at (English) and its website at under the Data tab, Lake Ontario outflow changes. 

Water levels on bothLakeOntarioand theSt. Lawrence Rivervary 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 m (247.3 ft) and above the lower limit (from April through November) of 74.15 m (243.3 ft) specified in the Orders of Approval, since regulation began in 1960, actual monthly levels have ranged from a high of 75.73 m (248.5 ft.) to a low of 73.82 m (242.2 ft) 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 (2 feet) in some locations.  


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

John Kangas: (312) 846-5348;

The International St. Lawrence River Board of Control was established by the International Joint Commission in its 1952 order of approval. The Board’s main duty is to ensure that outflows from Lake Ontario meet the requirements of the IJC order; it also develops regulation plans and conducts special studies requested by the IJC. For more information, visit To receive a weekly e-mail about water levels and flows in the Lake Ontario–St. Lawrence River system, please send a blank e-mail message to, with the word ’subscribe’ in the title and body of your message.