Tested Samsung's Gear sport open water swim setting tonight basically a glorified stop watch as it did not record any distance what so ever.
Been waiting for this open water setting for a while and I am bitterly disappointed.
I really don't want to get another device to record my open water swims but so far it's looking like that may be the case.
Same on my Galaxy Watch. No distance recorded, extreme calories recorded (3570) for 10 minutes swim. But map shows swimming route. Seams to be a bug here. Hope an update may solve it in future.