That's the second chapter of the Phoenix FD river tutorial. Here I'll create some additional elements (mist and vegetation) that will be used for the compositing.
The mist will be a separate aero simulation based on the water simulation from the first chapter (using splash particles as smoke emitters).
The vegetation will be just a geometry scattered with the "Object Paint" tool in 3ds max.
Finally I'll take the multichannel exr from the first chapter, divide it in render elements and then put it back together. I'll also use the MultiMatte render elements to setup some masks that will come in handy. And then I'll add the additional elements that I created in this chapter.
Hope you'll enjoy! :)