Freshwater mussels are among the most endangered groups of organisms on earth. They are particularly sensitive to environmental threats such as climate change, because of their sedentary nature. The freshwater mussel, Westralunio carteri, which is endemic to south-western Australia, has undergone a 38% reduction in range in the last 50 years, and with global climatic models predicting an increasingly warmer and drier climate in the region, reduced water flow presents a substantial extinction risk. In laboratory tolerance experiments, the mortality rate of mussels in drying conditions was much greater when they were exposed than when they were shaded. In both shaded and exposed environments, the mortality rate was also influenced by mussel movement. A survey of microhabitat occurrence found that the abundance of W. carteri was significantly negatively correlated with substrate grain size, which also may influence the vertical and horizontal movement of mussels. We discuss the implications of these results for the future survival of W. carteri.