I thought it must be alba or nigra, but then reading on NSW weed site (http://weeds.dpi.nsw.gov.au/Weeds/Details/147 ) , it doesn't mention alba, only nigra, cinerea and fragilis /rubens! Fragilis looks like alba to me. Any experts can comment?
From the Vicflora key it is somewhat more likely to be Salix nigra, with leaves green on both surfaces rather than strongly to weakly glaucous (bluish or greyish) underneath. Nigra leaves, however, are all narrow. Some of those in photo 2 may be too wide for nigra. The main character that differentiates Salix nigra from Salix x fragilis and Salix alba is the number of stamens per male flower. Salix alba has dull leaves that remain appressed hairy below. Salix x fragilis has leaves that are green and glossy above, soon becoming hairless below. Salix x fragilis is notorious for ithe brittle brittle junction between the twigs and the stem and the way the broken off twigs take root farther downstream. https://vicflora.rbg.vic.gov.au/flora/key/2278 The NSW Weedwise site only mentions specifically the willows regarded as the most serious pests.
Thanks for your comment and that link, v. useful. I will do some more work on salix in the burra creek as there seem to be a few species. Will have to wait till November for flowering though i suppose.