Caridina sp. is an atyid shrimp occupying coastal streams in south-eastern Queensland and northern New South Wales. Shrimps from two geographic regions in south-eastern Queensland were examined. An analysis of 7 allozyme loci showed very high levels of genetic differentiation among catchments (F ST = 0.65) with much lower levels within catchments. This indicates extremely limited dispersal among catchments with greater levels within catchments. The levels of genetic differentiation were even greater than previously reported for two other atyid shrimp species occurring in upland rainforest streams. Populations from the Noosa River were more similar to those from the Glasshouse Mountains than to those from the geographically closer Tin Can Bay streams. This pattern was remarkably similar to that of a fish species occurring in the same streams and may reflect a recent confluence of streams from the Glasshouse Mountains and the Noosa River regions.