Your Apple Watch is water resistant, but not waterproof. Water resistance isn't a permanent condition and can diminish over time. Apple Watch can't be rechecked or resealed for water resistance. The following can affect the water resistance of your Apple Watch and should be avoided:
- Wearing Apple Watch in a steam room
- Wearing Apple Watch models other than Apple Watch Ultra in a sauna
- Wearing Apple Watch Ultra in a sauna above 55° C (130° F)
For more info, see:
About Apple Watch water resistance - Apple Support
and:
Keep Apple Watch within acceptable operating temperatures - Apple Support
which says:
Apple Watch is designed to work best in ambient temperatures between 32° to 95° F (0° and 35° C).
Water temperature during underwater activities with Apple Watch Ultra: 32° to 104° F (0° to 40° C). I'm not sure how this applies to the series 8 watch.