It seems to be like LMB. Once you get it, you got it. I've killed it back several times around the edge of the ponds with Roundup but I don't use it in the water. I think they make special formulations of it for pond usage though. Mine always seems to grow back. I've had 2 ponds drained, cleaned out, deepened and made larger all the way around and the stuff showed up again in 2 years. I would have bet all traces of it and its roots had been eliminated. I now just live with it and only spot control it. Once it starts growing in warm weather, it seems to consume enough nutrients that it greatly diminishes the FA.