Consider Digitaria didactyla, Queensland Blue Couch. It has the advantage of being commercially available as seed or turf, as it is used as a lawn grass. It's a native.

I will just give you the genus names because in Melbourne the species will probably be different to those occuring up in QLD.

Close to the water
------------------
Carex sp.
Mentha sp.
Lobelia sp.
Typha sp.
Phragmites sp.
Lythrum sp
Pericaria sp
Myriophyllum sp.

Further up the bank
-------------------
Poa sp.
Einadia sp
Atriplex sp
Wahlenbergia sp
Calocephalus sp

Many others but these are a good start to provide cover and a bit of colour at the same time. Plant them densely for best results.

Myoporum parvifolium is a great native spreading groundcover that thrives on clay soils.