Hi JaneR. I've looked back as I was sure I'd seen it before at a different site in wodonga. This is what it got ID'd as then. Not sure if that helps or no. This the healthiest lot I've seen of it. Schoenoplectus tabernaemontani (River Club-rush)
ID as Bolboschoenus fluviatilis based on robust habit, height, noded stems, length of leafy bracts, general colour: however, spikelet shape (cylindrical) is a atypical, perhaps its an early stage.
TY JaneR. I will keep an eye on them from now on. They could have been planted but also could have come in the flooding (this site was underwater for a few weeks).