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Product Feedback - Apple
What watchOS version do you have?
From the 'Swimming' section in:
Workout types on Apple Watch - Apple Support
Here's how your Apple Watch measures each workout:
- Pool Swim: When you start a workout, be sure to accurately set the pool length to help your Apple Watch measure laps and distance. GPS isn't used during a Pool Swim, and water might prevent a heart-rate measurement, but calories, laps, and distance will still be tracked using the built-in accelerometer.
- Open Water Swim: GPS will only provide distance when you do a freestyle stroke. Water might prevent a heart-rate measurement, but calories will still be tracked using the built-in accelerometer.
Cellular coverage on cellular models of Apple Watch might be impacted during Pool Swim and Open Water Swim workouts.