General physical, chemical and biological information is given for a seasonally inundated billabong (Ox-bow Lake) of the Goulburn River near Alexandra. The microcrustacean fauna (Cladocera, Copepoda, Ostracoda) was rich in species, with 59 species in 44 genera being recorded over 1 year. Statistical analyses showed a significantly clumped distribution, and these apparent habitat preferences are interpreted with reference to the functional morphology of the animals and to weedbed characteristics.