I like to see ornamental grass around water features. Karl Forester gets large and looks great. I also have a meadow rue I like around mine. These are a bit smaller than what you are considering but may work as some "fill".

watercress grows great near moving water

i take the seeds and insert them into a small piece of those fiber rooting blocks then stuff them into roles in the rocks on my waterfall to help hide defects

it'll form a nice mat near the edge of the water and help keep the soil intact

thank you both for great suggestions! I have some grasses, but meadow rue is a good idea.
I really like the idea of how easy watercress will work too...sounds perfect for nooks and crannys
where did you buy your seed from?
thanks again
Debbie

Turtlehead, ligularia or goatsbeard are other choices for around a water feature.

I had both Turtlehead and Ligularia in my hands, but decided not to get them for now (although I love ligularia)...did pick up Goatsbeard and hopefully it will do alright considering it is more a shade plant and my planting areas around the waterfall is full sun. I tried to put it more behind a big boulder and where the moisture would stay more consistent. Guess next year will tell how well it does:)
Does anyone grow either Goatsbeard or Ligularia in full sun?

I hate to say this, but after the past two weeks of moving things around, digging, planting...I'm getting mighty sick of gardening! LOLS
I just keep reminding myself, that it will all be worth it next year. (I hope!)
Deb

One of my ligularias is in pretty much full sun and is doing not too badly. The area it's in faces east so it gets afternoon shade, but it's also dry, and it tends to wilt more than the heliopsis beside it. This is the first year blooming for all my ligularias and i really like them. The ones in the shade really brighten up the area!

Although my goatsbeard and ligularia are both in a shady position I understand that they will do fine in a sunny spot as long as the soil remains moist. Othello ligularia or one similar would probably be a better choice than the Rocket, I think. The Rocket tends to wilt even in the shade on a warm sunny day!

I did notice my shade ligularias wilting yesterday, but we've had some rain to perk it up. :)