One of the most crucial methods for understanding the state of any aquatic ecosystem is the use of test organisms such as fish or invertebrates. The water flea, Daphnia magna,is commonly used as a model species for ecotoxicological studies. In the current examination, D. magna neonates were exposed to concentrations of metals similar to those previously reported to occur in the ecosystem. The 48-h acute toxicity tests of FeCl₃, PbCl₂, and their mixture at different concentrations were applied to D. magna. The Probit analysis was used to calculate the 48-h median lethal concentration (LC₅₀) for each of Fe, Pb, and their mixture. The results revealed that Fe was more hazardous than Pb, with 48-h LC₅₀ values of 6.47 and 13.14mg/ l, respectively. Furthermore, the Fe-Pb mixture had a synergetic impact on Daphnia magna (mixture 48-h LC₅₀ was 3.9mg/ l). This study indicated that the realistic levels of Fe and Pb may trigger the lethal impacts of freshwater crustaceans, causing devastating impacts on the ecosystem and food web. These results may be valuable in elaborating water quality criteria and standards to protect the national aquatic systems that are drastically affected by anthropogenic industrial contamination. Because of the unexpected responses of multi-contaminant scenarios, there is a need for more thorough, environmentally appropriate research on the mixture impacts of the pollutants.