Lake Ontario water temperature
Lake Ontario, NW Lake Ontario Ajax · Lake
The current water temperature at Lake Ontario is 15.1 °C (as of October 16, 2026, source: NOAA NDBC).
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 1039 data points since August 17, 2026.
Lowest recorded value: 4.8 °C on October 10, 2026 · highest value: 22.9 °C on August 19, 2026.
In October, temperatures have ranged between 4.8 °C and 18.9 °C.
The current value is 1.0 °C above the October 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 15.1 °C. See live swimming conditions, weather and quality in the BrrChecker app.
How warm is the water at Lake Ontario?
Currently 15.1 °C (updated continuously).
How warm is at Lake Ontario in October?
In October, the water temperature recently averaged 14.1 °C.
When is the water warmest at Lake Ontario?
Across the measurement record, September is on average the warmest month (19.6 °C).
