Lake Ontario – St. Lawrence River System: Update and Outlook – HomeTown TV12

Lake Ontario – St. Lawrence River System: Update and Outlook

Lake Ontario – St. Lawrence River System: Update and Outlook

The first major spring storm pushed through the Great Lakes – St. Lawrence River basin this past weekend, bringing high winds and precipitation, raising inflows and accelerating the seasonal rise in water levels.

Strong, southwest winds rapidly increased water levels at the eastern end of Lake Ontario during the storm.  The wind, combined with rising inflows from the Ottawa River and other local tributaries, also raised levels in the lower St. Lawrence River, requiring a temporary reduction in the Lake Ontario outflow.

However, Lake Ontario outflows have been increasing again since, and are still well above average for this time of year, as the Board continues to get as much water off the lake as possible, while limiting downstream impacts.

Further increases are also expected, as the Ottawa River has reached a peak and is starting to decline.  This is expected to continue over at least the next few days.  Additional information can be found here:

Recent Conditions within the Lake Ontario – St. Lawrence River system:

  • Plan 2014’s Flood Limit (F-limit) continues to be the limiting factor for Lake Ontario outflows, and not the Navigation Limit (L-limit).
  • Lake Ontario’s lake-wide average level is roughly 75.33 m (247.15 ft) currently, which is now slightly below the level at the same time in 2017, and more than 30 cm (1 ft) below the 1973 record-high.

Future Conditions within the system:

  • Overall Lake Ontario outflows are expected to increase over at least the next few days as Ottawa River flows decline.
  • Lake Ontario outflow remains high currently, despite recent reductions necessary to address lower St. Lawrence River levels, and outflow will continue to be maximized to the extent possible.
  • The weather is expected to remain cooler and dry for several days.  There are no significant storm systems for at least the next week.

Shoreline impacts were reported across many areas of the Great Lakes during the April 13 storm, due to high winds, compounded by near or above record-high water levels on all but Lake Ontario.  Nonetheless, water levels of Lake Ontario are still well above their seasonal average, and strong winds can still cause significant damage and a surge in water levels.  Communities should continue to invest in long-term coastal resiliency measures to lessen the impact during high and low waters.

Please note that the Board has created a website page focused on the recent high-water events: (English) [ (French)]. All high-water related materials are now in one easily accessible place.

Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the Board’s website and posted to the Board’s Facebook page at (English), and more detailed information is available on its website at

Related posts

Leave a Comment