The present study explores the method of Environmental Protection Agency CE.P.A.) used for evaluation the toxicity of effluent into the receiving water. The study was applied on the effluent of pesticide manufacturing plant using short term chronic toxicity test method for evaluation the effluent toxicity. The a quatic organism Ceriodophnia Dubia used as a detector at different effluent dilutions. The results indicated that the productivity of C. dubia were reduced due to toxicity of the effluent under investigation. We recommend the method of E. P. A. for evaluation the toxicity of various effluents in water resources.