The Murray-Darling Basin (MDB) has a complex biogeographic history as it is surrounded by more independent river basins than any other Australian basin.  As a result portions of the aquatic fauna have a mix of relationships to all surrounding regions, as well as an endemic component.  Our project has three principal goals.  1) Is there an historical signature on biodiversity in the MDB and adjacent drainages that remains evident in the genetic structure of widespread species?  2) Are there concordant patterns of genetic structure across disparate aquatic and water-dependent organisms?  3) What are the impacts of dams on dispersal and degree of erosion of local genetic diversity of aquatic organisms?  We chose four unrelated aquatic species that were widespread acorss the MDB, but that lacked known complications due to introgression or presence of cryptic species: the fish Australian Smelt (Retropinna semoni), river turtle (Emydura macquarii), yabby (Cherax destructor) and shrimp (Macrobrachium australiense).  We are exploring patterns of genetic diversity using SNP variation from thousands of loci to address these three questions.