A technique is developed which offers both insights of field study and experimental control of the laboratory to measure at all trophic levels simultaneously the ecosystem response to biologically or chemically induced stress. Methods used by past investigators included model studies and studies of individual species as indices of environmental quality. Model studies fail to mirror dynamics in the natural habitat while studies of individual species provide only limited insight into population dynamics of the intact ecosystem. These methods make adaptation and extrapolation to field conditions extremely tendentious. This report describes observations of exogeneous chemical stress and the response of various aquatic plants and fish to various stresses. The initial stress tested relates to organophosphate insecticide, Diazinon, known for high selectivity for soil micoorganisms. Though the results of this study are preliminary and fragmentary, statistical analysis indicates a potential for computer simulated ecoassay. The novel use of an entire biota as a bioassay system rather than the classical resort to 'universal indicator species' is significant.