Physics Volume with a custom shape?

Hey Guys,

my swimmable area is defined by a Physics Volume where “Water Volume” is checked.
The problem is that i need a specific shape of it. I need the exact shape of the swimming area to be filled with the Water Physics Volume, and not only a boxy shape. The Brush Editing Tools are Crap.

Is it for example possible to use a Static Mesh and to convert it to a Physics Volume?
Thanks!
Gazu