Lower than average precipitation and winter snowpack runoff have resulted in decreased inflows to Lake Ontario. The reduced inflows have resulted in lower water levels on Lake Ontario and the St. Lawrence River. In response to these conditions, the International Lake Ontario St. Lawrence River Board decided to reduce outflows from Lake Ontario beginning April 10, 2021.
Under authority granted by the International Joint Commission (IJC), the board deviated from the plan during January and February this year to remove additional water from Lake Ontario. This decision was based on a risk analysis in December 2020 that showed approximately a 28 percent chance of water levels exceeding a damaging high water threshold in 2021. A total of 3.7 inches was removed from Lake Ontario to further reduce the risk of potentially damaging high water levels in late spring and early summer.
Due to the reduced spring runoff, the board has decided to reduce outflows below those specified by the plan to restore the extra water removed during the winter to Lake Ontario at a rate of approximately 0.8 inches of water to Lake Ontario per week for three weeks. After these three weeks, the board will revert to plan-prescribed outflows.
This strategy will allow Lake Ontario and Lake St. Lawrence water levels to increase more than they would under plan-prescribed flows over the next few weeks. It now appears likely that Lake Ontario levels will remain below the long-term average over the summer unless very wet weather occurs. Most forecast scenarios suggest that Lake Ontario levels will remain above critical low water level thresholds due to lower than average precipitation. Under this strategy, water levels in Lake St. Lawrence will experience short-term increases due to its position as forebay of the Moses-Saunders Dam. However, most forecast scenarios indicate dry conditions that will likely result in significantly below average Lake St. Lawrence levels this spring and summer.
The board will continue to monitor conditions closely through the summer. Should dry conditions persist, the board will meet again regularly to discuss potential actions to adjust outflows.
Information on hydrologic conditions, water levels, and outflows, including graphics and photos, are available at https://www.ijc.org/en/loslrb and posted to the board’s Facebook page.
Provided information
