Abstract: In order for water resource managers to effectively and efficiently react to algal growths that are prohibiting use of a lake, reservoir or stream, information must be obtained on the response of the specific algae in site waters to algaecide exposures. In the absence of this information, ineffective algaecides or excessive treatments may be implemented. Research on development of an efficient algaecide assay using site specific samples could contribute to better decisions regarding algaecide applications and increase margins of safety for non-target species. Since these laboratory experiments provide predictions of responses of algae in site waters to algaecide exposures, these predictions need to be confirmed in the field. Confirmation of laboratory responses with results from field applications of algaecides will increase confidence in the laboratory assay. Additional research on the responses of non-target species such as sensitive fish and invertebrates to algaecide exposures will permit better decisions by water resource managers regarding potential risks associated with a site specific application of algaecide. Research is needed to clarify this situation. Objectives of this research were to 1) develop a planktonic algal bioassay using site water and copper-containing algaecides, 2) measure responses of Lyngbya to algaecide exposures in the laboratory and the field, and 3) contrast responses of Pimephales promelas and Ceriodaphnia dubia to laboratory and simulated field exposures of copper sulfate and Cutrine®-Plus. Results of this research indicated that a smaller volume (> 100ml) and shorter duration (>72 h) of exposure can be used in planktonic algal bioassays using cell density and water from the site. Also, this research demonstrated that algaecide effectiveness in the laboratory, when site algae and water were used, can be observed at field sites. Confirmation of laboratory responses with results from field application of algaecides increases confidence in the laboratory assay. Results also indicated that less toxicity was observed in realistic declining exposures when compared to typical constant laboratory exposures. Laboratory studies that are predictive of responses of problematic algae to exposures of algaecides in field situations, and have been verified through field studies, can provide critical information for water resource managers to take effective actions.