.Map :: MoHAA Mapping

A map that I am working on has a dam with water flowing over it into a river. What is the best way to add an effect like fog or mist just in the area where the spill water meets the river? It needs to look like its about 6 feet high, 6 feet deep and 30 feet wide.

I think any of the fx_spray effects.

Just like they did for the shore on that single player mission with the lighthouse (m1l3c).

I never experiment with these effects though so I can't tell exactly how to use them.