Apple Watch going insane with swimming workouts?

[Pangalactic]

Went for very light swimming with hardly any effort in the sea - Apple Watch somehow measured I’ve burned 820 calories in 30 minutes after swimming 180 meters. Does anyone know if it’s a bug or some problem, or is Apple Watch not very good at this?

All the other activities (walking, elliptical, etc) seem to be at least somewhat accurate, but swimming for some reason makes the calories burnt go off the charts

 

[Spindel]

You don’t get a GPS signal if the watch is submerged. So swimming the distances get messed up unless you hold your arm above the surface.

This is a feature of radio signals and not really a AW problem.

 

[gtjeta]

It is extremely bad for breaststroke, both with respect to distance (GPS lock is lost and it does not interpolate to cover the gaps … which I find incredible), and specially regarding calories. Extremely low HR in breaststroke leads to almost double calorie consumption than higher exertion freestyle. I would say it multiplies the real calories almost by two. And it does the same in the pool.