The physical features of 20 streams inhabited by four recently discovered species of allopatric, non-migratory galaxiid fishes in the Taieri River, South Island, New Zealand were examined. Significant differences in particle size frequencies, combined waterfall frequency, channel depth variation and stream width: flood channel width ratios, indicated that Galaxias anomalus lived in low gradient shallow streams whereas G. depressiceps and G. eldoni occupied low to high gradient streams with more variability in depth. Climbing ability differed significantly among the species. Their allopatric patterns of distribution were, in part, the probable consequence of the abilities of G. depressiceps and G. eldoni to colonize areas that G. anomalus could not penetrate. Historical factors and reproductive biology of the four species are hypothesized also to be causal determinants of their current distributions.