The International St. Lawrence River Board of Control (Board) reviewed conditions in the Lake Ontario–St. Lawrence River system on August 10 and decided to continue to maintain outflows from Lake Ontario in accordance with those prescribed by Regulation Plan 1958-D.

This decision will pertain unless over-discharges are needed to meet critical hydropower needs, to maintain levels above 20.6 m (67.6 ft.) at Pointe-Claire on Lake St. Louis, or to allow incoming vessels to reach the Port of Montreal.  Any such over-discharges will be limited to no more than 600 cubic metres per second (cms) (21,200 cubic feet per second (cfs)) per day and 300 cms (10,600 cfs) per week.

The main considerations in maintaining this strategy are as follows:

Recent supply conditions

·        Precipitation on the Lake Ontario basin was near average in July, but the Lake Erie basin was wet.  In total, the water supply to Lake Ontario was below average.  

·        Although hot, dry conditions continue throughout the Great Lakes basin, the weather cannot be predicted with much certainty for more than a few days, so future water supplies from the Lake Ontario basin will remain unpredictable.

·        The outflow from Lake Erie into Lake Ontario for July was slightly below the average.

Current levels

·        Lake Ontario’s level fell in July and was 9 cm (3.5 in.) below the long-term average on August 10.

·        Lake Erie was 7 cm (2.8 inches) below average on August 10.

·        The level on Lakes Michigan and Huron remains well below average, so water supplies from those lakes to Lake Erie are expected to remain below average for the coming months.

·        Levels in the Montreal area were well below the average on August 10, and the level in Montreal Harbour was 2 cm (0.8 in.) below chart datum.

Plan 1958-D

·        Plan 1958-D is responding to the dry conditions and declining lake levels by gradually reducing the Lake Ontario outflow.

·        On August 10 there were 4.6 cm (1.8 in.) of water stored on Lake Ontario relative to the Plan 1958-D level.

Risk analysis

·        There is little probability that the Lake Ontario level between now and the end of December will be outside the range of levels specified in the International Joint Commission’s criteria for the regulation of Lake Ontario.

·        There is a significant chance that the Port of Montreal level will be below chart datum frequently in the coming months.

·        Outflows from the Ottawa River into the Montreal area are declining slowly.  However, as always, there is a significant degree of uncertainty regarding the outflows in the coming months.

Forecasts

·        If average water supplies are received over the coming months and Plan 1958-D outflows are followed, the level of Lake Ontario would continue to fall and, by the end of October, would be about 4 cm (1.6 in.) below average.

·        If conditions remain dry, the Lake level could fall to as much as 21 cm (8.3 in.) below average by the end of October.  However, this level is still well within the range of regulated levels specified by the criteria for the regulation of Lake Ontario.

·        If conditions turn very wet, the Lake level would decline more gradually and be 12 cm (4.7 in.) above average by the end of October, but, again, this level is well within the range of regulated levels specified by the regulation criteria.

·        With average supplies, the monthly level in the Port of Montreal is forecast to be below average, but above chart datum, in August and September.

The Board, in conjunction with its staff, will continue to monitor the situation, and will meet again in about four weeks to re-assess the situation—or earlier if there is a significant change in conditions before then.

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 www.islrbc.org/ or www.ijc.org (> Boards > International St. Lawrence River Board of Control).

Contacts:

Reg Golding, Ottawa, Ontario (613) 998-1408 e-mail: GoldingR@dfo-mpo.gc.ca

John Kangas, Chicago, Illinois (312) 353-4333 e-mail: John.W.Kangas@usace.army.mil