Spray them with Roundup, or glyphosate (generic of Roundup)
It kills cattails easy, and won't damage fish, frogs, etc.
If new ones come up, you spray them too.
The old fashioned way to remove cattails was to wade out and pull them up by the roots. You have to get all the root to stop them.
That's what we use. Anyone remember the old tree hugger guy on TV that used to eat cattails. Seems like his name was Eule Gibbons ?
