Perhaps it's not an emergent? It looks like that area is a bit flooded, I know some of the plants I've picked up as "emergents" aren't actually, but do well emerged.
They just happen to like high water, but often get a bit flooded during this season.
I'm not sure I'll be much help trying to ID it, but when I charge my phone later tonight I'll see if I can find anything lol
You may also have more luck using local library books over the internet.