I had some reed looking very much like what you have.the neighbors lake is surrounded by that stuff to the point that you can't get through it. It looks like cattail but never makes a top like cattail. I dug it up with my front end loader and killed it. Don't know what it's called but I don't want that stuff. It spreads by rhizomes under the mud as you can see in your pix, my opinion only your results may vary