Smoke grenades a plenty, though you don't think they'll have the same effect as, say, a squid's ink might. In which case, if you want to try sneaking up on this thing, looking for fauna to help might be an option.
A quick pair of Fix-It rolls if you want to use your lightsaber and/or gun underwater. Denzral is fairly handy with technology, so in no time at all your lightsaber is all set to use underwater (having rolled four successes). Your blaster, on the other hand, is less functional with a poorer roll of one success. It might misfire and become defunct during the fight.
They can let you have a few of those Gungan plasma balls. One of their warriors mentions they're better against machines but you can give it a try and see what happens.
And with all that, the Gungan council's guards escort you back to the otoh's entrance and more or less push you through the membrane and out into the open sea. It will be a decent swim out to the crevasse the monster resides in, but you can pace yourself and do just fine with the rebreather.
If you are feeling bad about killing the beast... something tells you that you shouldn't. You aren't sure what.