Freshwater systems are highly valuable natural resources, providing environmental, social and economic services. Perennial waterbodies provide protection of freshwater biodiversity during prolonged habitat or climatic disturbances. The extent of permanent waterbodies is driven by the highly variable flow regimes of Australia. River regulation, changing land use, natural hazards and anthropogenic climate change are some examples of increasing pressures on perennial waterbodies. Of concern is the increased frequency of cease to flow events during the Millennium Drought (~1997-2010) drought in systems what were traditionally considered perennial.  This raises the question of reliability of perennial systems during prolonged drought which could become more frequent in the future. Therefore, the aims of this study were to review data available on perennial systems and establish if perenniality is temporally variable due to drought. Data analysis revealed that the Australia wide perenniality dataset (GEODATA TOPO 250k Series 3) does not sufficiently represent all systems (with some missing or incorrectly classified). We also show that, while remote sensing technology has progressed, the use of long-term datasets required for analysing historical variability are constrained by spatial resolution. Therefore gauged stream data remains to be most useful source of information. However, in most regions suitable long-term stream data is unavailable, particularly those covering the droughts of the 1900s and 1940s, and some catchments completely ungauged. Therefore, a model was created for the Reedy Creek sub-catchment in Victoria as a case study to extend the flow history. The modelling shows that, during periods of very prolonged drought (e.g the Federation drought, WWII drought and the Millennium drought), watercourses previously defined as perennial fail to meet the definition. We suggest that given the extreme hydrologic variability in Australia, the definition of ‘perennial’ and ‘non-perennial’ may not be adequate and a new category of ‘temporally variable perennial’ needs to be developed.