The usage of herbicides is increasingly spreading both in the world and in Ukraine. Constant monitoring of this type of the polluting substances is one of the areas for maintaining the ecological security. It is significant for diverse environmental objects, especially for the surface water sources. Contemporary herbicides have a wide range of various mechanisms of action. In this regard, applied methods have to ensure the high level of sensitivity and reasonable specificity for measuring the excessive concentrations of herbicides in the environment. Besides, it is considerable to choose appropriate test organisms. They have to satisfy the list of requirements, while the most important one is that it would be a hydrophyte that has full contact with water. Therefore, the Elodea canadensis Michx. has been chosen by us as a test object. This species is a cosmopolitan and is widely used for the bioassay procedure. The system of biochemical transformations is one of the most sensitive links for the maintenance of the cell homeostasis. Typically, enzymes react to the stress-induced variation in environmental situation by modification of their activity. Consequently, this fact is used for the stress assessment of the organism. We have offered to measure the enzymatic activity of superoxide dismutase (SOD) as the most remarkable system biomarker on the toxic impact of the herbicides. The main function of SOD is the prevention of the growing oxidative stress in the cell. Thus, it can serve as an integral index that acts on the influence of varied chemical substances. For this reason, the aim of the research paper is to indicate the specific changes in the SOD activity of the Elodea canadensis’ cells in conducting the bioassay of the herbicides of varied groups. The aim was achieved through the investigation of the dynamical changes in the SOD activity of Elodea canadensis. The water plant had contact with varied groups of the herbicides in different concentrations. As a result, we have discovered the high sensitivity of the SOD activity of Elodea canadensis while being immersed into water with different herbicides. Hence, this test can be recommended for use to determine the contamination of water with pesticides. We recommend using a one-day experiment for the most representative results to explore the dynamical changes in the enzyme activity of elodea in herbicide solution. The elaborated bioassay method has the following advantages: quickness, accessibility and sensitivity. The absence of the specificity in similar studies can refer to disadvantages. Howsoever, it can also refer to advantages if the screening is conducted for a wide range of contaminations.