The abundance of epiphytic invertebrates living on both submerged and emergent macrophytes in lentic systems is influenced by a range of environmental features at both spatial and temporal scales. Such features include water chemistry, habitat complexity, hydrology and external influences such as climatic cycles. Dugays 2 billabong is a floodplain lake on the highly regulated, mid-upper Murray River in southeastern Australia. Giant rush (Juncus ingens N.A. Wakefield) is the dominant habitat feature in this billabong. This plant is a simple, single-stemmed, densely packed emergent macrophyte that fringes the littoral margins. The macrophyte habitat available to epiphytic invertebrates in this billabong is highly variable through time largely due to the variable water levels imposed by the regulated river channel for downstream irrigation needs, particularly through summer. To investigate both spatial and temporal patterns in the epiphytic invertebrates of Dugays 2 billabong, invertebrates were sampled within giant rush stands on five occasions over one year. Spatial variability in epifaunal density was generally low, while temporal densities were highly variable through time. Spatial patterns of invertebrate abundance revealed few associations with habitat structure or water quality, apart from those associated with water depth, particularly when sampling had been preceded by fluctuating water levels. High temporal variability in assemblage structure of the epifauna reflects the high background environmental variation that occurs in this system. Copyright © 2007 John Wiley & Sons, Ltd.