International Lake Ontario - St. Lawrence River Board

Board aims to return to Plan flows soon


The International St. Lawrence River Board of Control (Board) recently reviewed conditions in the Lake Ontario-St. Lawrence River system and has decided to return to Plan flows as soon as possible. The Board will also continue to permit additional under- or over-discharges that may be necessary to address unforeseen critical conditions.
Recently, the Board deviated from Plan flows to assist in flood management both upstream in Lake St. Lawrence and downstream in Lake St. Louis. Under-discharges occurred during the first Ottawa River peak flows of mid-April, resulting in the Lake Ontario level 3.2 cm (1.3 in.) higher than they would have been under continuous Plan flows. This water will be released by over-discharges as conditions permit. The Ottawa River is expected to have a second significant peak, which may again require reductions in Lake Ontario outflows to prevent flooding downstream, resulting in additional water being stored on Lake Ontario.

After starting April 2014 below average, Lake Ontario is currently above its long-term average level for this time of year. The level on April 27 was 75.00 m (246.06 ft), 4 cm (1.6 in) above average. This is well within Lake Ontario’s 1.22 m (4 ft) range, being 37 cm (14.6 in) below the lake’s upper limit. The level at Lake St. Lawrence, just upstream of the Moses-Saunders powerhouse, was about 8 cm (3.1 in) below average. Downstream, the level at Lake St. Louis was 30 cm (11.8 in) above average; 6 cm (2.4 in) below the flood Alert level, and at Montreal Harbour, the level was 36 cm (14.2 in) above average, 2.37 m (7.8 ft) above chart datum.

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 Maps & Data tab, Lake Ontario outflow changes.

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 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;
Kyle McCune: (513) 684-3014;

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.