In full sun, I used in the 70s: sunny 16 (1/ASA at f16) for surface to 4+ feet. After 5 feet go to f11 until 10-12 feet then another notch. Use C-41 or B&W film so any weird light changes will be absorbed by latitude. With soft shadow bright, cloudy overcast, and heavy overcast or open shade; use f-11, f-8, f-5.6. This is if you don't go beyond 4 feet; if so then adjust as above.
Film fan has a good point about stand development but in most underwater cases contrast is diminished already so you will be lucky if you get into a high contrast scene but you possibly might where you are going.
If you do choose stand development, scan so you can correct contrast in your editing program.