Apple Watch Series 2
When you start a swimming workout, your Apple Watch automatically locks the screen with Water Lock to avoid accidental taps. When you're done, turn the Digital Crown to unlock the screen and clear any water from your Apple Watch. You hear sounds and may feel some water on your wrist.
To manually clear water from Apple Watch, swipe up on the bottom of the watch face to open Control Center, tap Water Lock, then turn the Digital Crown to unlock the screen and clear water from the speaker.