Open Water Data

Water Temperature

Water temperature is an influential factor that affects if, when, where and how people swim, including whether or not they may prefer a wet suit.

Cold Water Swimming Considerations

Swim Season

The Ontario swim season starts in mid May and continues until late September.  During this time water temperatures can range from 10°C / 50°F to 24°C / 75°F.  Great lake temperatures tend to be somewhat lower.


For newcomers a reasonable target to aim for is to be comfortable at a water temperature of 15°C / 60°F.  This may mean starting training over short periods at colder temperatures than this outdoors, then you will become more acclimatized to the cold water.  When training outdoors, always have a swim buoy and safety boat or swim partner(s).

Swim Speed

Among other open water swimming factors, water temperature can impact swim speed.  Swimmers may not be able to swim as fast in cold outdoor water as they do in warm pool water as a result of energy expenditure being inversely proportional to the temperature of the water to cover a given distance in a given time.  Because of this and other open water swimming factors, the duration of an outdoor swim will typically be greater than pool swim times.  As a result of these slow down factors, it is essential to train for a distance greater than that which you are going to attempt to swim.

Weather Conditions

Water temperature can be heavily influenced by local weather conditions, cold up-swells and/or a local stream entering the lake.

Data Sources

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