International Lake Ontario - St. Lawrence River Board

Board planning its return to Plan Flows


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 by the weekend. To assist boat haul out in Lake St. Lawrence, which has been low recently due to higher than average outflows, the Board has decided to under-discharge by 600 m3/s (21, 200 ft3/s) relative to plan-specified flows for one day starting the weekend of 4 October. The following weekend, the weekend of the Canadian Thanksgiving, the Board will gradually increase outflows to restore water levels relative to Plan 1958-D. Once there, outflows will remain at Plan-specified outflows. The Board will also continue to permit additional under- or over-discharges that may be necessary to address unforeseen critical conditions.

Lake Ontario is currently above its long-term average level for this time of year. The level on September 24 was 74.71 m (245.11 ft), 1 cm (0.4 in) above average. This is well within Lake Ontario’s 1.22 m (4 ft) range, being 66 cm (26.0 in) below the lake’s upper limit, and 56 cm (22.0 in) above the lake’s lower limit. The level at Lake St. Lawrence, just upstream of the Moses-Saunders powerhouse, was about 26 cm (10.2 in) below average. Downstream, the level at Lake St. Louis was 16 cm (6.3 in) above average; at Montreal Harbour, the level was 1 cm (0.4 in) above average.

The Board, in conjunction with its staff, continues to monitor the system. 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.