Geosmin is produced by several phototrophic and heterotrophic taxa. This secondary metabolite can impart an earthy taste and odor to water resources. To reduce algal populations and associated biosynthesis of geosmin, copper sulfate and other copper-containing algicides are often applied to aquatic systems. Cultures of the bacterium Streptomyces tendae and the fungus Penicillium expansum grown on increasing concentrations of copper sulfate accumulated more biomass than untreated controls, indicating that these heterotrophic cultures were not markedly susceptible to this algicide. Cultures of Streptomyces albidoflavus treated with increasing concentrations of copper sulfate accumulated less biomass than untreated controls. However, copper-treated mycelium of each taxa investigated contained greater concentrations of geosmin than untreated controls. In addition, there was not a significant interaction between in the amount of biomass or geosmin accumulated by cells exposed to 0 and 0.5 mg l−1 copper sulfate over increasing dosages of zinc sulfate. If field populations exhibit similar responses, application of copper sulfate to aquatic systems may contribute to geosmin biosynthesis by certain taxa.