Allow me to "wade in".

Having skipped all the personal back-n-forth, I'd like to make the distinction between pool water & ocean water.

Pools are good for physical therapy & exercizes for elderly/disabled folk mainly due to resistance & weight suport.

Oceans are good for MA training the following reasons:
1) running on the sand (technically not in the water but as long as you're there...)

2) Kicking in knee-deep water (works on balance & bringing the knee up & out of the water as opposed to dragging your leg up)

3) Punching waves in waist-deep water (again, balance & timing to strike @ the precise moment)

4) Controling (not holding) your breathing

5) Rapid foot-work in knee-deep water (advancing, retreating, tai sabaki) while maintaining balance

6) Kumite/Yakusoku kumite in knee-deep water (training not to flinch even if your face is splashed)

7) Finally...if you begin just before sunrise, it tests your determinhation to train - especially when it's cold (internal/fighting-spirit)

(#8 is an optional don't need pee-breaks, just dribble down your leg...who's to know?)