Lake Ontario water temperature
Lake Ontario, Oswego · Lake
The current water temperature at Lake Ontario is 20.5 °C (as of September 20, 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.
.jpg){kind=link}
Measurement series & statistics
This measurement series includes 292 data points since July 23, 2026.
Lowest recorded value: 20.5 °C on September 20, 2026 · highest value: 25.0 °C on August 14, 2026.
In September, temperatures have ranged between 20.5 °C and 23.2 °C.
The current value is 1.7 °C below 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 20.5 °C. See live swimming conditions, weather and quality in the BrrChecker app.
How warm is the water at Lake Ontario?
Currently 20.5 °C (updated continuously).
How warm is at Lake Ontario in September?
In September, the water temperature recently averaged 22.2 °C.
When is the water warmest at Lake Ontario?
Across the measurement record, August is on average the warmest month (23.3 °C).
