I think it depends on what type of plants they are and how much the water level fluctuates.
The predominant plant looks to be rice cutgrass, which prefers wet, fertile, silty, soil. It gets aggressive in disturbed wetlands, which my renovated pond is.
Knobber, do you know how deep the unwanted plants are? I raise and drop a small pond of mine, and grasses sometimes die, but the stalk remains. I would think they'll drown out, but like Sunil said, it depends.
They are growing anywhere from 0 to 30 inches of water. Too early to tell on this new pond who much the water level will fluctuate.
I think this grass is here to stay. It is just a matter of the depth of water in which it can tolerate.
