St. Lawrence River Ice Formation Begins, Lake Ontario Outflow Reduced – HomeTown TV12

St. Lawrence River Ice Formation Begins, Lake Ontario Outflow Reduced

St. Lawrence River Ice Formation Begins, Lake Ontario Outflow Reduced

Cornwall – Cold weather has caused ice formation to start at critical areas on the St. Lawrence River, requiring Lake Ontario outflows to be temporarily reduced in order to reduce the risk of ice jams.

Cold temperatures yesterday and overnight caused water temperatures to plunge along the St. Lawrence River.  With milder temperatures forecast later this weekend, high outflows from Lake Ontario were maintained and slightly increased yesterday, in an attempt to break up and discharge any ice expected to form at the Beauharnois Canal overnight.  However, despite this, the first ice boom at Beauharnois had filled with ice by this morning.  Ice booms help facilitate ice formation, which prevents major ice flows and ice jams from occurring.

Outflow reductions from Moses-Saunders Dam will be made today to reduce stress on the ice cover downstream at Beauharnois. Hydro-Quebec is already passing higher flows through the north channel that runs parallel to the Beauharnois Canal in order to the limit the reductions required and ensure outflows can remain as high as possible.

While Lake Ontario remains above its long-term average, regulated outflows will remain as high as feasible based on river conditions, and will be increased again as soon and as rapidly as possible.  Once a solid ice formation is established, higher outflows will be passed under the solid ice cover.

As a result of the Lake Ontario outflow reductions, residents around Lake St. Lawrence, immediately upstream of Moses-Saunders Dam, are being warned to expect increasing water levels over the next few days.

As water supplies to Lake Ontario remain very high, Lake Ontario levels are also expected to begin slowly rising.  The Board will be monitoring conditions closely and adjusting flows with the intention of passing the highest possible outflows, while ensuring ice conditions are maintained and do not result in safety concerns.

Since construction of the St. Lawrence Seaway and Moses-Saunders Dam in the 1950s, it has been necessary to reduce Lake Ontario outflow as ice forms on the St. Lawrence River. This reduces the risk of ice jams that can damage infrastructure and cause severe flooding, by slowing down the current.  Slower currents keep ice at or near the surface, and, weather permitting, helps them form into large pans that accumulate, solidify and build a stable ice cover.  Once established, outflows can be safely increased to pass under the solid ice cover, allowing higher outflows later in winter.

The Board, in conjunction with its staff, continues to monitor conditions on an ongoing basis. 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

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