OOC: Misha (and all other characters) cannot 'charge', because a) the water is considered 'difficult terrain' and b) As the monster attacke from behind the party, and Misha was up front, Misha does not have a clear path to the Vodyanoi.
Nantonaku-You can run up to the monster.
Also, I am assuming movement is at 1/2 rate in the water. I'm going to query that in the rules forum.
On mapping, movement and so forth: I do use a grid map to keep track of positioning. I will try to move your characters, based on your posts, in as good a position as possible. If the enemy incures an Attack of Opportunity, I will assume you make it (state so if you prefer otherwise).
If you want your character to cleave if possible, please post so. It's obviously irrelevant here, but keep it in mind.