This report details the first detection of invasive freshwater shrimp in the south-west of Western Australia, a region recognised for its biodiversity and the vulnerability of its endemic species. The species was detected as part of biosecurity surveillance of Perth’s freshwater lakes. The introduced specimens were tentatively identified morphologically as Caridina indistincta, and then confirmed by molecular analysis as “species B” of that taxon, part of a species-complex native to eastern Australia. Phylogeographic analyses were then used to narrow down the likely source population to a small area of south-eastern Queensland, over 3500 kms across the continent from the invasion sites. The potential source area is heavily involved in the trade in freshwater species for aquaria and recreational fish stocking. This information will help in identifying the precise invasion vector and could thus allow more targeted management measures to prevent future imports of exotic aquatic invasive species.