This large reed-like plant has rich dark green, thick & tubular leaves and seed heads are clearly visible. It thrives in water, but can handle drying out to some extent. It has not multiplied as prolifically in this semi-permanent dam as the other 2 main marsh plants here (reported at sightings 4647199 & 4647203).
Oh great . If feasible and timely, please do close–up macro photograph seeds as well. As in many species in this sedge botanical family Cyperaceae the seeds as well, have more diagnostic features .
I suspect the seed heads will have lasted this long (i.e. since mid Dec), but it may have already shed its seeds. There's rain in the area right now, so I'll be waiting for a finer day to go and check on it's current state.
I'll give you a heads up when I have more photos to contribute.