[clothahump]

Are you referring to Parrots Feather.
We have found that it does excactly what you are saying, and yet if you just throw a handful into a pond it grows like mad, perhaps it should be grown as a floating plant.
Remember if you are getting rid of it, do not put into your local water ways, it is a pest that is very hard to get rid of.
I think it is a major problem in Australia,if Kitten reads this perhaps she could respond. 8)