If you've taken a stroll along Lake Ontario throughout the past couple of weeks, you might've noticed that the lake's water level has visibly dropped since the summer. 

However, this isn't a cause for alarm, as water levels are typically always lower throughout the fall and winter seasons, and noticeably higher during the spring and summer. 

Despite what you may have noticed, water levels through the Great Lakes have actually been above their long-term averages since spring 2023, with seasonal declines beginning in June. 

The International Lake Ontario-St. Lawrence River Board also ensures that outflows from the lake each continue to meet the requirements of the International Joint Commission's Orders of Approval. 

The Board consistently monitors water levels against Plan 2014, which is a set of rules that governs Lake Ontario outflows through the Moses-Saunders Dam located near Massena, N.Y., and Cornwall, Ont. 

Water Level in Lake Ontario
byu/ThePhilosophistt intoronto

The above-average water levels on Lake Ontario at the beginning of September 2023 actually exceeded the threshold that triggers what's known as the "September Rule" within Plan 2014. 

The September Rule requires increases in flow through the Moses-Saunders Dam when levels measure above 74.8 metres at the beginning of September in an effort to lower them below this figure by the end of the year. 

The Lake Ontario outflow may also be modified more frequently throughout the rest of the year depending on the conditions in the lake and the St. Lawrence River. 

On Sept. 1, 2023, the daily mean water level on Lake Ontario was 74.98 metres. 

But as of Sept. 30, water levels on Lake Ontario declined to 74.8 metres — the threshold at which the September Rule no longer applied. This means outflows through the dam will be increased above the flows until the amount of water that was held back on Lake Ontario is discharged downstream. 

By Oct. 3, 2023, the daily mean water level on Lake Ontario had lowered 74.73 metres, again decreasing to 74.48 metres by Nov. 22. In comparison, the lake's daily mean water level on Nov. 22 in 2021 was 74.87 metres. 

It's important to note that the ability to regulate the outflow from Lake Ontario still doesn't mean that full control of lake levels is possible.

This is due to the many major factors that affect water supply to the Great Lakes, including precipitation, evaporation and runoff, which can't be controlled and are difficult to accurately predict.