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Outflow remains at seasonal record high, Lake Ontario continues to decline

To provide the highest attainable relief to all interests, both upstream and downstream of the Moses-Saunders Dam, outflows remain at record-high rates for this time of year, eclipsing the outflows released at this same time in any other years dating back to 1900.  As Lake Ontario continues its seasonal decline, the outflows now and for the foreseeable future will remain at the maximum rate possible given shoreline property owners’ interests and safety considerations throughout the Lake Ontario – St. Lawrence System.

The board considers outflow limitations defined and prescribed in the approved regulation Plan 2014 when setting the outflows during extreme conditions.  During extreme conditions the Board is designated with the authority to deviate from plan flow to provide relief to one or more interest groups. In doing so, the Board is required to weigh the impact of providing relief against the benefit. Outflows of this magnitude are subject to multiple constraints of the Lake Ontario – St. Lawrence system. The Board reached consensus that the current outflow is the highest currently possible, which provides the most relief to shoreline property owners upstream and downstream and provides safe conditions for all other interests.  Information on the outflows can be found on the Board’s website https://ijc.org/en/loslrb/watershed/flows.

Significant impacts of the 2019 high water event throughout the Lake Ontario-St. Lawrence River system are due to record-high water supplies into Lake Ontario over the 8-month period from November through June, and the record volume and peak flows in the Ottawa River from April through May.

The unprecedented conditions and record water levels that followed caused damage to many residents and communities over the summer and some of these impacts continue today, even with flood conditions diminished in the system. It will take time – even with well above average outflows – for the water levels to go down as inflows from Lake Erie continue to be well above average.  Water levels are primarily driven by water supplies, not by the outflows.  The outflows are also constrained by physical limits of the river system.

Continuous outflows of 10,400 m3/s were possible this summer with a series of additional safety measures required by the St. Lawrence Seaway administration. This flow was based on the record high Lake Ontario elevation; however, as the lake levels decline flows must be reduced to maintain the same balanced level of impact. River velocities increase as the same volume of water passes through a lower and narrower river.  Lake Ontario has been declining relatively rapidly in recent weeks, making it necessary to reduce outflows and manage dangerous river currents.

Given the current conditions, velocities are higher than normal throughout the river and they are causing potentially unsafe cross-currents with erosion impacting many interests in the St. Lawrence River. Sustaining or increasing velocities would cause conditions to become much worse.  Even with the weekly reductions, the outflows will remain at the highest rates ever for the time of year to provide all possible relief to shoreline property owners both upstream and downstream.

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 https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard (English), and more detailed information is available on its website at https://www.ijc.org/en/loslrb.