Scientific article published in Hydrobiological Journal. — 2014. — No.3. - T. 50. — C. 108-120. A model experiment conducted in mesocosms installed on a fish pond allowed to reproduce the features of methane formation in the conditions of a powerful one-time impact on the aquatic ecosystem of one of the most toxic heavy metals - cadmium. Intake of cadmium in quantity, Substantially higher than , causes the death of hydrobionts, their gradual destruction and sedimentation to the bottom of mesocosms , which leads to a decrease in the content of oxygen dissolved in water , and as a consequence to the activation of anaerobic processes , including methanogenesis, in sediments and water.