I have something growing in my pond and can't seem to remember the name. It looks like a bulrush with pink flowers on it. My dad cleaned out his Koi pond and told me to plant it. Worked for a few years until it has started to spread. Now I want to kill it off before it starts growing. I know this is limited info. I do recall reading about it in the forum years ago. I have tried google and can't seem to find a pic.

I think I figured it out. It is flowering rush.