Why does the Apple Watch not monitor heart rate during swimming?

Hi

Apple Watch Series 2 does measure heart rate during Pool Swim and Open Water Swim workouts recorded via the Workout app, but water may affect the sensor's performance. Apple Watch will still track calories using the built-in accelerometer.

To include heart rate as one of the metrics that is displayed during the workout:

• On your iPhone, in the Watch app, go to: My Watch (tab) > Workout > Workout View > Multiple Metric > select Pool Swim or Open Water Swim.
• Tap Edit (upper-right) > select up to five metrics, including Heart Rate > tap Done (upper-right).

For the best performance from the heart rate sensor during swimming workouts, be sure to wear your Apple Watch snugly on the top of your wrist. Apple suggests that you consider tightening the band before starting a workout and loosening it again afterwards.

More information:

• Work out with your Apple Watch - Apple Support
• Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support

Check out this article > https://www.macrumors.com/2016/09/23/apple-watch-swimming/