Operating under water in 3.5

[Balor01]

Soon, my PC-s(lvl 4) will face the fact that they must dive into depths of a lake. What kind of shenanigans can I expect regarding breathing and moving/fighting underwater? What should I watch out for? (I know underwater combat is covered in Core, but I would just like some opinions from playgrounders)

(there are paladin, sorcerer and cleric)

[Andreaz]

Have more than one source of not drowning, particularly if they're both mundane or if you will be up against beings used to the fact that drowning is a very effective way to kill enemies that drown.

If you can't bypass the mobility restrictions(first that comes to mind, and one of the most pervasive ones, is Freedom of Movement). If they are restricted, a good way to keep the fight on their terms is to fight in closed spaces; a wide open field is the whole "mr fighter can't fly to swing his sword" mockery tuned up.

Those with Alter Self can work almost effortlessly under water for 40 minutes/(casting*person) at level 4. If they know they'll be underwater a lot, they better bring a dozen scrolls/wands of that.