That seems very high to me unless you're doing an awful lot of swimming. I just looked at a recent bicycle ride: 34K with a total riding time of 1:44, average heart rate of 119 BPM and only 665 active calories. (This was a casual ride, not a workout.)
By the same token, on a day that I did three 50 minute dives from a live aboard I got credited with 1260 active calories. And I hardly swim at all. (It's not a lap pool, right?) I wore the watch over a Sharkskin rash guard, so I know heart rate wasn't being measured.
I'm glad the watch gives you some workout credit for diving, but I'd like to know how the active calories are being calculated.