Most garmin watches with a single sensor, altimeter temperature barometer, fail after some contact with water. If you swim with a garmin watch with that sensor, eventually it will fail. At first it gives fluctuating readings of elevation, finally failing completely. There is no cure except to replace the sensor. On a Fenix this is easy, as there are screws holding everything together. On a Forefunner, they are glued together and there are no screws. This is an extremely common fault. The more you swim, the quicker your barometer altimeter temperature combined sensor will eventually fail. Interesting that you won't see this common failure mentioned as a common failure on popular so called watch review blogs - so it is obvious that they don't like to comment on it. Nearly $1000 on a watch that has such a common failure quickly despite being advertised as being compatible with swimming is a disgrace.