Macroinvertebrates were sampled from riffles upstream and downstream of the Blue Rock Dam construction site and inundation area in late November/early December 1979 (before construction) and 1982 (late in construction). Changes in the downstream fauna were much less than at some other large dam sites in Australia, probably because of improved erosion control. At the downstream sampling stations the total number of taxa collected was similar in both years, but there was a 30-40 per cent reduction in faunal density; no significant change in density occurred at the upstream station. Multivariate analysis showed that the degree of change in faunal composition between years was similar at upstream and downstream stations. The proportion of fine (<4 mm) inorganic sediment in the streambed increased significantly at downstream stations over the study period, while there was no signficant change upstream. Silt (<250μm) also increased significantly downstream, but never exceeded 1 per cent of inorganic bed material.