Thanks for sending the photo - I think your lovely water feature would be enhanced by some flowing Japanese Forest Grass to soften and hide the edges. This golden grass will disappear in the winter so add some evergreen black mondo grass and for a different texture the golden lamium groundcover and if you have at least half a day of sun the golden and creeping thyme can go around the edge of the pond. Don't wait for these plants to fill in but hide the plastic edge of the pond and waterfall with some flat stones sitting on top of the plastic rim. The plants can then flow over the rocks. It will be lovely. Keep growing, Marianne Binetti