I´ve found this: "The device needs one or two weeks of training history, including activities with VO2 max. results from running or cycling, to determine your training status".
Now that we can record our heart rate in the pool,.. why couldn´t give some importance to swimming activities? Maybe I´m not aware of some technical issues that make imposible to do that but, well, ain´t this a triathlon watch? Why running and cycling but no swimming?