Even when wearing a full set of equipment that is WATER_FRIENDLY, going underwater results in morale penalties.
If the morale from the Wet status becomes negative, it will remain negative until you fully dry out. Afterwards you may get the morale bonus from water again.
I’m a diver and in my opinion you should still get penalty’s. its stinking cold up here in the north and you are definitely not happy one you get out of the water.