In my opinion, another good idea maybe to make lightsabres 'circuit out' underwater, or when the blade comes in contact with water.
page is useful in background information.
I think fighting with lightsabres underwater is too unrealistic. This may also be the case for blaster shots; they could burn-up after a meter or so in water, meaning they're unable to get the upper hand over Jedi wielding sabres.
I have a feeling most people won't like this idea. I haven't read about any breakthroughs in Lightsabre technology allowing them to duel with lightsabres underwater.
A good example of this is in Aliens Versus Predator 2. The Predator's cloaking device would circuit out in water, making the game more realistic and tactical.
The other alternative is allowed more
ability to fight underwater. Maybe even some code can be added, to allow specific models to not drown. Mon Calamari can hold their breath underwater longer than any human. This will probably be abused by everyone putting their models in as immune to death underwater, making it a bad idea in the long term.
Hope my aquatic ideas help.