Is it a good idea for a lifeguard to wear an apple watch series 3 to work?

Yes.

There are also worn by professional swimmers.

Hi

Whether or not to wear Apple Watch during lifeguarding duties is a matter of personal preference.

Whilst Apple Watch Series 3 is suitable for use when shallow water swimming, keep in mind that:

• After contact with anything other than fresh water, the watch, band and your wrist should be cleaned with fresh water and dried.
• Apple Watch can be damaged by contact with abrasive materials, such as sand.
• Your Apple Watch may potentially become dislodged during rough contact with third-parties, such as when responding to an emergency.
• Some users have reported experiencing issues with the Sport Band having come undone during swimming in the ocean, so you may prefer to use a band with a different type of fastening.

  Leather and stainless steel bands are not water resistant and should not be worn when swimming.

• The functions that are available on Apple Watch when it is used away from the paired iPhone vary depending on various factors, as detailed here:
  • About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support
  • How to use your Apple Watch without your iPhone nearby - Apple Support

More information:

About Apple Watch water resistance - Apple Support

Important handling information