I agree about all of the confusion. I have seen the totally aquatic slender spikerush AND the emergent terrestrial plant that grows where it only requires "wet feet".
Those seem like two different environmental niches to me. I suspect different species and perhaps even different genera.
Maybe you should post it in the "Controlling Unwanted Plants" forum? It sounds like it is well established in your pond. If it is hurting your fishing, then my 2 cents is to start battling it.
