Thermal stratification in dam impoundments can result in a colder, bottom hypolimnion layer and a warmer, surface epilimnion layer of water. Cold water pollution (CWP) occurs when water is released from the hypolimnion resulting in temperatures significantly lower than the natural temperature of the river downstream of the dam. The abrupt drop in water temperature can be as much as 15°C lower than the natural river temperatures and the decrease in temperature can extend hundreds of kilometres downstream from the release point. The conundrum is that water is often released to achieve environmental water flows, sometimes to trigger fish migration, yet these releases can result in decreases in water temperatures that may severely impact fish swimming performance and fitness. Here we utilised an experimental, lab-based approach to examine how rapid reductions in water temperature, of a magnitude reported from the Murray Darling Basin, affect the performance of four native Australian fish species that occur in this system. We investigated both short term (acute effects) and chronic exposure to decreases in temperature on maximum sustainable swim speed (Ucrit), routine metabolic rate, and maximum metabolic rate. A key objective was to assess whether Australian fish species have the capacity to compensate for the depressive effects of low temperatures via thermal phenotypic plasticity (thermal acclimation). Surprisingly, the species studied showed limited capacity for thermal acclimation which has substantial implications for the management of cold water releases from large dams and the passage/migratory capabilities of native fish.