Reeds, rushes, cattails, etc usually do not grow in the middle of a stream or river. They grow on the banks where the moving water is slowed by shallowness. It takes a bit to pull off reeds in the middle - with your water fall so close it will be difficult to pull that one off.
Rocks inside of the waterfall just doesn't work - due to the transparency even the most place rock totally in the waterfall looks like it is floating in space. The best way to make it work is to use something like rock chunks and "build" up the boundary.
For games you would make a custom rock chunk, change it to ramp or pathing blocker to remove the hp and ability to attack it.
also, your waterfall is pumping out way more water than that narrow stream can handle.
I've made a quick water fall as example (attachment) - it is by no means complete - this is only a "rough" version. I bet you can see the rocks that I did not lower yet, and besides the cliff walls needs to be covered, hidden, blended something.
Note how the basin that the water fall dumps into is wider, it leaves the impression that that much water can flow. If I were to take this further I would build up "rock chunk" boarders on both sides narrowing the channels that the water fall is falling in.
Things like floating debris, lily pads need to be "hooked" on something that obviously would not move due to the water. Such as a log, or a group of rocks - just floating there we expect the flow of the stream to "push" the floating debris downstream until it does snag on something.
Stacking waterfalls does not work - the waterfall doodad has a "top" and a bottom animation that creates the effect of water on a surface - You can customize and stretch as much as you need. And example is in my second attachment.
In object editor I made a copy, held down the shift key and selected Maximum Scale and typed in 500. I plopped the doodad then I hit enter and increased the 5 to 500 - The first waterfall is the extreme one - the second has its base water spread animation just above water level, the other has it way up in the air - although the water fall is on its "bottom".
Others have great success in stretching the x &/or Y while reducing the z forming long wide stretches of "rushing" water.
Cheers