I've been swimming with my apple watch for several months. Heart rate monitoring works (not sure if it's less accurate somehow? but it works), but there's nothing out there for tracking laps. The screen is also basically impossible to use while the buttons are too easy to trigger accidentally, so I start a workout and lock the watch, then unlock after I get out of the pool.

I was considering writing my own app for laps, and I do believe there was a story shortly after the watch came out where someone else worked on an app like that, but obviously it would not be allowed on the store. :(