Funny I always want a stream flowing thru my own property too. Usually a natural pond and a stream on a property with a house means too much money for us.
I tell them No
Seriously it has never been a issue for me They will eat a few things. I have water parsley which grows very easy. I break sections off and put it under a rock so they can eat it and boy do they wipe it out. They tend to leave the lilies alone. My main 2 planting areas are like a bog design but are not filters at all. I have a stone wall and they are filled with gravel so the fish can't get to the areas. The remaining plants are it pots. I do have butterfly koi and goldfish which is the better mix for plants. The butterfly koi are not as bad at eating the plants for some reason.