This paper presents development stages of water bodies’ ecological status integral index. The surface water acute toxic effects for different taxonomic level test-objects (Daphnia magna Straus, Chlorella vulgaris Beijer, Paramecium caudatum Ehrenberg) are used as one of the priority feature properties. Ecological status assessment is based on the composite indices method. The specific combinatory water pollution index (SCWPI), the Pantle-Buck saprobity index in the Sladecek modification (for phytoplankton) and toxicological characteristics are the priority features for this. The biotest indicators are Daphnia magna death rate, Chlorella vulgaris optical density , Paramecium caudatum toxicity index. Using feasibility of toxicological characteristics for water ecosystems ecological status integral assessment, along with hydrochemical and hydrobiological characteristics is tested in terms of the lakes in Pskov region and the Petrokrepost bay of Ladoga lake. As a result of ecological status assessment the Bolshoj Ivan lake in Pskov region was qualified as well-saturated. Other water objects were estimated as having satisfactory conditions. Ecological status of the Petrokrepost bay of Ladoga Lake (in 2013) was estimated as limitary between two classes: “satisfactory” and “unsatisfactory”.