Yeah, those drowned dead sure lay the smack down
When I've run into packs of them, I basically have three strategies that have helped:
1) TURN UNDEAD. Nothing like making them flee so you can attack their swollen backsides
2) Area-of-effect spells: Curse, Entangle, Malison, Slow. Anything to weaken their attacks.
3) Summoned creatures, especially fire elementals. Let them take the beating!
Just finished the Burial Isle last night, I hope that's the last I'll see of those critters!