Thank you for your crits!!! I really appreciate that. You're right, the particles are a bit too large. The problem is, if I make them smaller, the mesh will be too "thin", i. e. there still aren't enough particles for that. And I can tell you, it's a lot. It took almost an hour to transform the particles into an .obj-file.
Anyway you're right, there have to be some changes. I'll see what I can do. Probably a little more postwork regarding the waterfall would be the best.