[@Gordian Nought]
I'll take care of the rolls, but if you want to know how I do it, I will use Blood Bowl scatter mechanics. First a roll to see if it scatters, if it does the "where" will be answered with another series of rolls. We'll see what will be hit and what not. Once the accuracy is taken care of, anyone that may or may not be under the water will DEX save. On success, no damage. On a failure, I'd like to say 1d4+1 frost or bludgeoning damage as an improvised weapon. Let me get onto it.