The release of cold water from the base of large dams known as ‘thermal pollution’ can become a major problem for ‘warm water’ ecosystems. Downstream effects on many species extend for hundreds of kilometres, and in the MDB, several thousand kilometres of river are affected. Impacts can include direct loss of species, reduced spawning ability, loss of critical life stages such as eggs or larvae, temperature shock, reduced growth rates, delayed maturity, loss of cues to migration, increased stress and susceptibility to disease. Also, cold water favours many introduced species, and can cause changes that significantly alter the primary production of an ecosystem.
A workshop held at Lake Hume on 18-19 June 2001 brought together a broad cross-section of interests, stakeholders and professionals with expertise and first-hand experience of the problems presented by thermal pollution. Over the two days knowledge about impacts was shared, gaps in understanding highlighted, and known and potential solutions to the problem discussed.
Evidence for the negative impacts of thermal pollution on river health, native species and ecological communities is compelling and steps need to be taken to address the issue. Negative impacts also extend to the general community in terms of fish availability and habitat loss. There are now a range of solutions available for fixing the problem, which warrant high priority and the investment of adequate resources to ensure that the appropriate dams are modified or managed to address the problem. Thermal pollution should be listed as a threatening process under relevant legislation, and all future water infrastructure decisions on rivers need to include thermal mitigation measures.
Implications for native fish
Thermal pollution has the potential to cause localised extinctions of some species; kill eggs and larvae outright; reduce physiological processes such as reproduction and growth, reduce the ability to combat infections; and introduce cold water shock. The most pronounced effects of cold water pollution happen during the spring/summer months when irrigation releases occur, and at which time many native species are spawning.
Phillips, B. (Ed). 2001. Thermal Pollution of the Murray-Darling Basin Waterways. Workshop held at Lake Hume 18-19 June 2001. Statement and Recommendations plus supporting papers. Inland Rivers Network and World Wide fund for Nature Australia, 2001.
Astles, K.L., Winstanley, R.K., Harris, J.H. and Gehrke, P.C., 2003. Experimental study of the effects of cold water pollution on native fish. NSW Fisheries Final Report Series No. 44. ISSN 1440-3544.
Preece RM and Jones HA 2002, ‘The effect of Keepit Dam on the temperature regime of the Namoi River, Australia’, River Research and Applications, 18:397–414.
Ryan, T.J. and Preece, R.M. 2003, Potential for thermal shock in the Murray-Darling Basin, a report to the Murray-Darling Basin Commission (Natural Resources Management Strategy), Victorian Department of Sustainability and Environment, Heidelberg, and NSW Department of Sustainable NaturalResources, Parramatta.
Sherman, B 2000, Scoping options for mitigating cold water discharges from dams, Consultancy Report 00/21, CSIRO Land and Water, Canberra.
Sherman B, Todd CR, Koehn JD, Ryan T 2007, Modelling the impact and potential mitigation of cold water pollution on murray cod populations downstream of Hume Dam, Australia. River Research and Applications 23:377-389.