If you want to kill it back, I would use herbicides that contain glyphosate. In my pond, (I am not a licensed applicator), I typically use Roundup if only very little of it gets in the water. This water plantain plant always finds a way to colonize bare soil areas around water.
I used to get concerned and worried about this plant and would kill this stuff. Not any more. It is a good shoreline plant; it never becomes a problem, does not grow very tall or thick like cattails, holds the soil to the bank, provides good cover for frogs and best of all does not grow in water deeper than 6" or 8". Plus it does not look all that bad. If I don't want it in some areas, in those areas, I plant water iris or short (slender) spike rush (Eleocharis acicularis).
PS: In MI, You probably have cut-grass (Leersia oryzoides) not saw grass.
