Daphnia magna is the only (OECD) approved aquatic study organism to experimentally study the hazardous level of the water bodies and therefore to prescribe the lethal dose of metals. A study is envisaged and carried out to evaluate the toxicity of bimetals namely, Potassium dichromate (K2Cr2O7), Zinc Sulphate (ZnSO4.7H2O) and Cupric Sulphate (CuSO4.5H2O) on the cladoceran, Daphnia magna. The toxicity was observed to find the LC50 at known physico-chemical parameters and at regular intervals of time (h). Results revealed that at a frequency of 24 h exposure, the LC50 was found to be 3.5mg/L for potassium dichromate, 4mg/L for zinc sulphate and 4mg/L for cupric sulphate on Daphnia magna. The exposed Daphnia magna were subjected to histopathological studies using Transmission Electron Microscopy (TEM) and the pictograms revealed intense deposits of metal (Cr > Zn >Cu) around the arterial system which would have been the reason for mortality of Daphnia magna.