98% sure it's coontail, but a close-up of a small portion of stem & leaves would help confirm that it isn't Chara.
Whether coontail or Chara, neither ranks highly on grass carps' food-preference list. They'll eat either, but not as aggresively as more palatable plants.
Depending on your objective and the dynamics of the pond's water (static vs transient), various aquatic herbicides offer differing degrees of control; I.E. either short-term and somewhat selective control in targeted areas using spot-treatments (with relatively frequent applications) - or longer-term and relatively non-selective control throughout the entire waterbody with a single annual treatment (in static-water ponds).
IMO, grass carp sometimes prove worthy as "vegetation-maintenance tools", but rarely bring an extensive coontail infestation under control in the absence of excessive stocking-rates or the assistance of herbicides.

Kelly Duffie
Cypress, TX