It might be subsp. hydrophhilum, which also occurs in the ACT on stream banks. There is not enough information in the photos for me to tell either way.
I am not familiar with this species or subspecies: I opted for subsp. cinereum for its leaf shape, and the low number of coarse teeth. But the distinction between the two subspecies is not strong (at least, when based on info in Flora Vic on-line).