Daily plankton collections were taken from a billabong of the River Murray for two weeks prior to inundation in March 1990, and continued for ten days after flooding. Quantitative responses of the plankton community and the component species were analysed against measured environmental variables and between species. Rotifers and copepod nauplii were the predominant net plankton (> 53 µm). Significant negative or positive responses to inundation were detected for most common taxa of 63 rotifer species recorded. A four-fold dilution from intrusion of river water masked rapid population increases. Opportunistic responses to inundation appear to be a survival strategy in the highly unpredictable billabong environment.