It was found that fish were frequently denied access to upstream habitats in all four stream systems by the presence of physical barriers. Instream habitat characteristics correlated poorly with fish distribution, while the location of physical barriers matched the major dissimilarities in fish community composition between sites in all cases. The flume experiment found that Galaxias truttaceus and Galaxias maculatus have the same maximum sustained and burst swimming speeds. Salmo trutta and Pseudaphritis urvillii also had the same maximum sustained speeds, P. urvillii did not burst swim. The two galaxiids had significantly different swimming abilities from S. trutta and P. urvillii, with the galaxiids being the poorer swimmers.

Predictions made from the flume swimming experimental results were validated using the culvert experiment, at least for high water velocities. Culvert slope and perching were found to be a major cause of culverts preventing fish passage, with slopes above 2% or perch sizes >10cm being barriers to all Tasmanian fish species examined. Greater than 70% of culverts investigated in the study area had slopes over 2% and 50% of culverts had perch sizes >10cm. Culverts pose a major threat to the conservation status of Tasmanian stream fishes.