In the summer period, North Pine Dam in southeast Queensland, Australia, is used as a supplementary source of drinking water for the city of Brisbane. Relatively high concentrations of geosmin and methylisoborneol (MIB) are frequently detected in the water in summer. The abundance of cyanobacteria (= blue-green algae) that are known to produce these compounds, is generally low, which suggests that the odours are produced by other organisms. In this short study, we examined the abundance of geosmin- and MIB-producing actinomycetes in the water and sediment of the reservoir. The results show that actinobacteria actinomycetes are included in the taxonomic group of Actinobacteria) made up 18 to 24% of all bacteria in the dam water during a period of relatively high geosmin and MIB concentrations. The high density of actinobacteria in the dam suggests that these bacteria may be more dominant in production of geosmin and MIB than previously expected, and that they should be included in future studies of odour problems in freshwater reservoirs.