Hi Marc - we have been there often, and going in 2 weeks again
It is mostly for sun protection you see full sleeved suits - but yes, the water is a bit cold, but because of the warm air you dont need much usually.
That said, if you have to swim and drift for a long time, you would like some suits yes.
A 3/2 full suit is more than sufficient.
Many uses shorty's or short sleeved or short legged.
A few are in shorts but with a neo top then.
Others use their "old" and cold (because of the age of the suits, and if they are often cold even when warm) 5/3 full suits.
Extremely individual, you can use anything actually, down there