Mercury pollution is a global environmental problem. An alternative to the chemical method of removing mercury from the aquatic environment is the phytoremediation process, based on phytofiltration, phytoextraction, and phytovolatilization techniques. The study showed the effectiveness of phytoremediation with plants Lemna minor and Salvinia natans carried out in monoculture systems and mixed cultures. We used Hoagland's mercury-contaminated liquid medium: 0.15 mgHg/dm3, 0.20 mgHg/dm3 and 0.30 mgHg/dm3. The relative growth rate of plants in the control samples was 0.04–0.07 g/gd. In the presence of mercury for monocultures, observed a toxic effect in the form of growth stimulation, and the relative growth rate reached 0.12 g/gd. The bioconcentration factor was the highest on the 7th day of mercury exposure and was 216–856. The efficiency of mercury removal from the substrate in the phytoremediation process was 96 %. The total protein was increased for Lemna minor by 34 %, Salvinia natans by 84 %, and in mixed culture by up to 99 %. Also, the total chlorophyll increased for Lemna minor by 14 % and for the mixed culture by up to 60 %. For Salvinia natans, the total chlorophyll decreased by 53 %. The biochemical changes may have been a toxic effect of mercury in the environment.