Somehow it needs to involve sharks. It is, after all, based on water. Lasers...sharks...
I'm starting to see this spell forming up nicely
Seriously though, ya about every 6 months or so an ice dot, fire dot, fire nuke, etc.. is suggested. Its not a terrible idea, but it is way more complicated than most folks think initially. If we could additionally add Sisslak/Bane/Yoppa like ice damage, there'd be many encounters where that sum of our dots would be overpowered, given the current resist balance in the game.
High damage fire and ice are pretty much exclusively a mage/wiz/necro thing. Most mobs are susceptible to those lines, probably because the classes that own them are dps classes. Mobs that resist PR/DR are part of the game balance I think. We're pretty lucky to have gotten a magic dot line.