The waterfall eyecandy trick is very useful in scenarios involving rivers. You will need to be very patient to get the proper results, so this may take some time.
1. You must create cliffs in the union of both rivers, like this:
As you can see, there are two very importants cliffs that would help in the illusion. (those with arrows)
2. After you delete the cliff in the middle (use delete button in "units" section), and unite the river, head to the Gaia objects.
3. As you can see, we use lot of water rocks (small and large). Try to put some in the begining of the and in the end of the waterfall, we know that there are a lot of rocks in Waterfalls
also try to mix between small water rocks and big ones, like after you make a big water rock, put some smalls in the end of it. Here is a sample of what your's should look like:
4. Stay in the Gaia objects, this time you must use the "Plant (Aquatic)" and start placing some in the begining of the waterfall, in the end, and also a few in the middle. (maybe one each side)
5. After that, start the mix between Water deep and shallows:
First make that part of the river entirely water shallow and then you must use water deep, use it in the begining of the waterfall and in the end, try to put it near the water rocks, maybe inside of them, but let some shallow in the middle, that would create an illusion.
In the end, if you have followed the five steps carefully, you should have something similar to this:
A beautiful and realistic eye-candy waterfall!
Contact the author, Tartarus at firstname.lastname@example.org.