Lochow Pond Management says 30%. I hate grass carp. Our lake is 70 years old. Grass carp stripped it of all native vegetation and invasive Alligator grass took over. Grass carp won't touch that stuff. I'm now trying to re-establish beneficial vegetation and even after 20 years I still have to fence everything to keep the grass carp from destroying it. Vegetation is the base of the food chain,unless you want to feed forever.