OSWEGO — Heavy rainfall over the past month caused Lake Ontario water levels to rise more than five inches and international regulators say outflow deviations are set to expire.

The International Lake Ontario-St. Lawrence River Board (LOSLRB) — a regional sub-unit of the U.S.-Canadian International Joint Commission, which oversees shared waterways between the two countries — said this week the Great Lake’s waters rose above the low water mark that allows deviations from the water management plan known as Plan 2014. Outflows from Lake Ontario through the Moses-Saunders Dam, which had been among the lowest in years over the past few months, are set to increase after heavy rainfall in recent weeks followed months of persistent drought conditions.

International regulators say increased outflows are likely to decrease water levels on Lake St. Lawrence and increase levels on Lake St. Louis. Lake Ontario water levels remain dependent on precipitation and inflows from Lake Erie.

“The above average rainfall the first two weeks of July was unexpected but truly benefited the region”, said Steve Durrett, U.S. co-chair of LOSLRB. “There is an unpredictable natural supply of water for the Great Lakes and it is important to recognize the full range of high and low water levels that have historically occurred within Lake Ontario.”

Lake Ontario water levels fell below historical averages in January after several years of high water and flooding that included multiple high-water records in 2017 and 2019. The easternmost Great Lake reached a record 249.08 feet in June 2019, just two years after setting the previous record.

Throughout 2021, Lake Ontario has remained below historical averages and remains more than 7 inches below the historical average for mid-July despite recent heavy rains.

International regulators noted despite the recent above average rainfall in the Lake Ontario-St. Lawrence River system, drought conditions have persisted in much of the Great Lakes and St. Lawrence River watershed. U.S. drought monitoring continues to show abnormally dry to moderate drought conditions within the basin, both upstream in Lake Erie and Lake Ontario and downstream along the St. Lawrence River.

Precipitation over the past two weeks increased Lake Ontario waters by nearly three inches, according to the IJC. Seasonal declines in Lake Ontario waters typically would have started by this time of year, but the lake instead has risen over the past month.

For much of the past year-plus, international regulators have deviated from the much-maligned Plan 2014, which many property owners and local officials blame for flooding in 2017 and 2019. The IJC has often granted LOSLRB authority to deviate from the plan, but as of July 17 the most recent deviation authority expired causing a return to the outflows prescribed in Plan 2014.

A return to the prescribed flows of Plan 2014 means an increase in outflows, and as noted an increase in water levels on Lake St. Louis and at the Port of Montreal ranging from roughly 4 to 6 inches. Lake St. Lawrence is likely to decrease by roughly 6 to 8 inches, according to regulators.

LOSLRB said the board would continue to monitor weather forecasts and water supply conditions and re-evaluate the regulation strategy regularly. For more information on hydrologic conditions, water levels and outflows, visit www.ijc.org/en/loslrb or the board’s Facebook page at https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard

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