Abundance is tentative, there may be more. A good survey with someone who knows the species better would be a good I reckon
No need to confirm, I fully intend to delete (and reupload) this sighting
Barb, this record is a bit downstream of the one you mentioned above. Most of the above photographs seem to show stems with empty fruit heads; it might be that the stems were broken further upstream and swept or blown down. The 3rd photo of a strap-like leaf is puzzling and I think not related to Water Plantain at all; the leaves of Water Plantain look different see https://canberra.naturemapr.org/species/501.
This appears to be part of the same few plants reported for 24 August, just a bit older and a bit more battered by high flows. The leaves in photo 3 look like Plantago.
I suggest editing the frames to concentrate on those that show the fruiting head clearly