Quick question

[NTJedi]

You can remove them from the game by using the map edit commands to setup a super powerful independents inside the water provinces. Personally I recommend including independent SCs to keep water provinces off limits. Just make sure the army has plenty of food otherwise they will starve and eventually be vunerable.

If you're playing SP games it's even more important to not use water provinces for DOM_3 since water mages can no longer enter provinces the majority of land AI opponents never go into the water.