That's some thick stuff, Gleeser. What treatments did you try other than the grass carp? Haven't seen Kelly post in a while...your problem looks like a real challenge. Is there a lot of fertility in the water? Is there significant run-off from nearby land that is highly fertilized? That may be the cause...fertilizer was the cause in my case.

If you stocked 40 grass carp in 8 acres, that isn't nearly enough for a problem of this magnitude. On a smaller scale, treating with Reward a couple of times in the year and following that up with young hungry grass carp finally worked for me on a bad pondweed invasion. The grass carp prefer new growth and won't touch old growth if there is anything else to eat. So, killing it back some and then letting the grass carp loose on the new growth, worked for me....but now I have too many grass carp in the effected pond!