New Zealand's two species of freshwater parastacid crayfishes have allopatric distributions, with one species in the North Island and northwestern South Island and the other in the eastern and southern South Island and Stewart Island. This gives the appearance of a vicariance event driven by uplift of the Southern Alps beginning in the Pliocene, and of former land connections across both Cook Strait and Foveaux Strait. However, separation of the two species may date from before the Southern Alps were formed. A diverse series of historical geological events is invoked to explain details of the distributions of these two species. Absence of Paranephrops from intermontane valleys of eastern flanks of the Southern Alps is notably different from patterns seen in freshwater fish species.