Craig Hockenberry has published an in-depth report on the capabilities of Apple Watch while swimming in the Pacific ocean:

After the watch shipped, I discovered that I wasn’t the only person interested in the watch’s ability to be used during swim workouts. Ray Maker at the DC Rainmaker blog did a series of tests, including diving off a 10 meter (33 foot) platform and 40 meter (130 foot) pressure test. The Apple Watch passed these tests with flying colors, and along with the research below, I was convinced I wouldn’t have any problems. So far, that analysis has proven correct.

I suspect that the watch’s water resistance has been undersold by Apple just like battery life: it’s better to under-promise and over-deliver. Still, it’s a personal decision on whether you want to ignore Apple’s recommendation. You’re not likely to get much sympathy at any subsequent trips to the Genius Bar.

Now that we know the Apple Watch can go in the water, how does it work while submerged?

There’s a lot of interesting data in this post and some good ideas for how controlling workouts on the Watch could be improved in future versions of watchOS. It definitely seems like Apple hasn’t added proper support for swim workouts because they don’t want to advertise the device as being completely waterproof yet.

See also: Dr. Drang on stress corrosion cracking and Apple Watch.