Lake Ontario water temperature
Lake Ontario, West Lake Ontario (OMECP) · Lake
The current water temperature at Lake Ontario is 18.6 °C (as of September 18, 2026, source: GLOS).
Lakes stratify in summer: bathing-warm on top, markedly colder a few metres down. Measurements are taken at the surface — right where you swim.
Measurement series & statistics
This measurement series includes 170 data points since August 24, 2026.
Lowest recorded value: 5.7 °C on August 31, 2026 · highest value: 20.4 °C on September 9, 2026.
In September, temperatures have ranged between 7.7 °C and 20.4 °C.
The current value is 2.5 °C above the September average of this series.
Nearby waters
More measuring points: Lake Ontario
Frequently asked questions
Can you swim at Lake Ontario right now?
The current water temperature is 18.6 °C. See live swimming conditions, weather and quality in the BrrChecker app.
How warm is the water at Lake Ontario?
Currently 18.6 °C (updated continuously).
How warm is at Lake Ontario in September?
In September, the water temperature recently averaged 16.1 °C.
