Tip 4: How to pause your swim workout in waterproof mode
Normally, to pause a workout, you just swipe right and tap the pause button. But you can’t do that during a swimming workout because waterproof mode disables the touchscreen. Fortunately, Apple still lets you pause a workout by pressing the Digital Crown and side button at the same time. In watchOS 4, this even works with third-party fitness apps like MySwimPro.
If you have screenshots enabled on your watch, it’s a little annoying, because the two-button press also triggers a screen shot every time you pause your workout. So you might want to turn that off. (In the iPhone Watch app, go to General > Enable Screenshots.)
Tip 10: How to finish your workout when the touchscreen is disabled
This is actually harder than it sounds. If you scroll the Digital Crown to turn off waterproof mode while you are still in the water, it can be very tricky to operate the touchscreen, because it is usually still covered with water droplets that can mess with the screen’s sensors. There is always the risk that you might delete the workout accidentally. Fortunately, Apple removed the risky Discard button from watchOS 4, but the possibility remains with some third-party apps.
A much better approach? Leave the waterproof mode on and just pause the workout using the two-button press until you get out of the pool and toweled off. Then disable waterproof mode and finish the workout when you are all nice and dry.
Above from:
https://www.cultofmac.com/524027/apple-watch-swimming-tips/