Apple ULTRA watch - why does it not record a swim accurately - it leaves out section of the swim

Hello Avner1,

You may want to look over and follow the steps on this page: Get the most accurate measurements using your Apple Watch - Apple Support. This is information provided by Apple on how to ensure your Apple Watch is tracking your daily activity and workouts accurately. It provides detailed steps for how to do the following:

1. Keep your personal information up to date.
2. Make sure that you earn Move and Exercise credit.
3. Make sure that Wrist Detection is on.
4. Check the fit of your Apple Watch.
5. Get the most accurate heart rate measurement.
6. Choose the best workout.
7. Calibrate your Apple Watch.

You may also find the details on this page helpful for how and why to calibrate the Apple Watch: Calibrate your Apple Watch for improved Workout and Activity accuracy - Apple Support.

You can calibrate your Apple Watch to improve the accuracy of your distance, pace, and calorie measurements. Calibrating your watch can also help it learn your fitness level and stride, which improves accuracy when GPS is limited or unavailable.

We hope this information helps you out.

Best wishes!